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< h2 > Foundation< / h2 >
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<!-- Weave of 'Linked Lists and Stacks' generated by 7 -->
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< ul class = "crumbs" > < li > < a href = "../webs.html" > Source< / a > < / li > < li > < a href = "index.html" > foundation< / a > < / li > < li > < a href = "index.html#2" > Chapter 2: Memory, Streams and Collections< / a > < / li > < li > < b > Linked Lists and Stacks< / b > < / li > < / ul > < p class = "purpose" > A simple implementation for single-linked lists of objects allocated by Foundation's memory manager, and for last-in-first-out stacks of same.< / p >
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< ul class = "toc" > < li > < a href = "#SP1" > § 1. Implementation< / a > < / li > < li > < a href = "#SP6" > § 6. A function call API< / a > < / li > < li > < a href = "#SP7" > § 7. A macro-ized API< / a > < / li > < li > < a href = "#SP9" > § 9. LIFO stacks< / a > < / li > < / ul > < hr class = "tocbar" >
< p class = "inwebparagraph" > < a id = "SP1" > < / a > < b > § 1. Implementation. < / b > Basically, there's a head structure, which points to a chain of body structures,
each linking to the next. But to reduce memory manager overhead, we're going to store
the first few body structures inside the head structure: that way, for a list of just
a few items, only one call to the memory manager is needed.
< / p >
< pre class = "definitions" >
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< span class = "definitionkeyword" > define< / span > < span class = "constant" > NO_LL_EARLY_ITEMS< / span > < span class = "plain" > < / span > < span class = "constant" > 32< / span >
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< / pre >
< pre class = "display" >
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< span class = "reserved" > typedef< / span > < span class = "plain" > < / span > < span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > {< / span >
< span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > first_list_item< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > last_list_item< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > linked_list_length< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > < / span > < span class = "identifier" > early_items< / span > < span class = "plain" > [< / span > < span class = "constant" > NO_LL_EARLY_ITEMS< / span > < span class = "plain" > ];< / span >
< span class = "constant" > MEMORY_MANAGEMENT< / span >
< span class = "plain" > } < / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > typedef< / span > < span class = "plain" > < / span > < span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > {< / span >
< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "identifier" > item_contents< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > struct< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > next_list_item< / span > < span class = "plain" > ;< / span >
< span class = "plain" > } < / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > ;< / span >
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< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The structure linked_list is private to this section.< / p >
< p class = "endnote" > The structure linked_list_item is private to this section.< / p >
< p class = "inwebparagraph" > < a id = "SP2" > < / a > < b > § 2. < / b > < / p >
< pre class = "display" >
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< span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::new< / span > < span class = "plain" > (< / span > < span class = "reserved" > void< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > ll< / span > < span class = "plain" > = < / span > < span class = "identifier" > CREATE< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > );< / span >
< span class = "identifier" > ll< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > = < / span > < span class = "constant" > 0< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > ll< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > ll< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > ll< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The function LinkedLists::new is used in < a href = "#SP7" > § 7< / a > , < a href = "#SP10" > § 10< / a > .< / p >
< p class = "inwebparagraph" > < a id = "SP3" > < / a > < b > § 3. < / b > The following runs in constant time, i.e., performs no loops. In general we
want speed rather than memory efficiency.
< / p >
< pre class = "display" >
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< span class = "reserved" > void< / span > < span class = "plain" > < / span > < span class = "functiontext" > LinkedLists::add< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > , < / span > < span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "identifier" > P< / span > < span class = "plain" > , < / span > < span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > to_end< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "null list"< / span > < span class = "plain" > );< / span >
< span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > item< / span > < span class = "plain" > = < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > < < / span > < span class = "constant" > NO_LL_EARLY_ITEMS< / span > < span class = "plain" > )< / span >
< span class = "identifier" > item< / span > < span class = "plain" > = & (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > early_items< / span > < span class = "plain" > [< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > ]);< / span >
< span class = "reserved" > else< / span >
< span class = "identifier" > item< / span > < span class = "plain" > = < / span > < span class = "identifier" > CREATE< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > );< / span >
< span class = "identifier" > CREATE< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > );< / span >
< span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > item_contents< / span > < span class = "plain" > = < / span > < span class = "identifier" > P< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > to_end< / span > < span class = "plain" > ) {< / span >
< span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) {< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
< span class = "plain" > } < / span > < span class = "reserved" > else< / span > < span class = "plain" > {< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "plain" > } < / span > < span class = "reserved" > else< / span > < span class = "plain" > {< / span >
< span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > ++;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The function LinkedLists::add is used in < a href = "#SP7" > § 7< / a > , < a href = "#SP10" > § 10< / a > .< / p >
< p class = "inwebparagraph" > < a id = "SP4" > < / a > < b > § 4. < / b > Because of the direction of the links, only removing from the front is quick:
< / p >
< pre class = "display" >
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< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::remove_from_front< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "null list"< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "empty list can't be popped"< / span > < span class = "plain" > );< / span >
< span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > top< / span > < span class = "plain" > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > top< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > --;< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > top< / span > < span class = "plain" > -> < / span > < span class = "element" > item_contents< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The function LinkedLists::remove_from_front is used in < a href = "#SP5" > § 5< / a > , < a href = "#SP10" > § 10< / a > .< / p >
< p class = "inwebparagraph" > < a id = "SP5" > < / a > < b > § 5. < / b > It's rather slower to delete from a known position in the middle:
< / p >
< pre class = "display" >
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< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::delete< / span > < span class = "plain" > (< / span > < span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) < / span > < span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "null list"< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > ((< / span > < span class = "identifier" > N< / span > < span class = "plain" > < < / span > < span class = "constant" > 0< / span > < span class = "plain" > ) || (< / span > < span class = "identifier" > N< / span > < span class = "plain" > > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > )) < / span > < span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "index not valid"< / span > < span class = "plain" > );< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > == < / span > < span class = "constant" > 0< / span > < span class = "plain" > ) < / span > < span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "functiontext" > LinkedLists::remove_from_front< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > );< / span >
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< span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > item< / span > < span class = "plain" > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "identifier" > first_list_item< / span > < span class = "plain" > ; < / span > < span class = "identifier" > item< / span > < span class = "plain" > ; < / span > < span class = "identifier" > item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > ) {< / span >
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< span class = "identifier" > N< / span > < span class = "plain" > --;< / span >
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< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > == < / span > < span class = "constant" > 0< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > == < / span > < span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > ) < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "identifier" > contents_deleted< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > -> < / span > < span class = "element" > item_contents< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > = < / span > < span class = "identifier" > item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > --;< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > contents_deleted< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< span class = "plain" > }< / span >
< span class = "identifier" > internal_error< / span > < span class = "plain" > (< / span > < span class = "string" > "index not found"< / span > < span class = "plain" > );< / span >
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< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The function LinkedLists::delete is used in < a href = "#SP7" > § 7< / a > .< / p >
< p class = "inwebparagraph" > < a id = "SP6" > < / a > < b > § 6. A function call API. < / b > < / p >
< pre class = "display" >
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< span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "functiontext" > LinkedLists::len< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > L< / span > < span class = "plain" > ?(< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > ):0;< / span >
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< span class = "plain" > }< / span >
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< span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::first< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > L< / span > < span class = "plain" > ?(< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > ):< / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::entry< / span > < span class = "plain" > (< / span > < span class = "reserved" > int< / span > < span class = "plain" > < / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > if< / span > < span class = "plain" > ((< / span > < span class = "identifier" > N< / span > < span class = "plain" > < < / span > < span class = "constant" > 0< / span > < span class = "plain" > ) || (< / span > < span class = "identifier" > L< / span > < span class = "plain" > == < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ) || (< / span > < span class = "identifier" > N< / span > < span class = "plain" > > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > linked_list_length< / span > < span class = "plain" > )) < / span > < span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > I< / span > < span class = "plain" > = < / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > first_list_item< / span > < span class = "plain" > ; < / span > < span class = "identifier" > I< / span > < span class = "plain" > ; < / span > < span class = "identifier" > I< / span > < span class = "plain" > = < / span > < span class = "identifier" > I< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > )< / span >
< span class = "reserved" > if< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > -- == < / span > < span class = "constant" > 0< / span > < span class = "plain" > )< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > I< / span > < span class = "plain" > -> < / span > < span class = "identifier" > item_contents< / span > < span class = "plain" > ;< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::last< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list< / span > < span class = "plain" > *< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > L< / span > < span class = "plain" > ?(< / span > < span class = "identifier" > L< / span > < span class = "plain" > -> < / span > < span class = "element" > last_list_item< / span > < span class = "plain" > ):< / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::next< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > I< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > I< / span > < span class = "plain" > ?(< / span > < span class = "identifier" > I< / span > < span class = "plain" > -> < / span > < span class = "element" > next_list_item< / span > < span class = "plain" > ):< / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
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< span class = "reserved" > void< / span > < span class = "plain" > *< / span > < span class = "functiontext" > LinkedLists::content< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > I< / span > < span class = "plain" > ) {< / span >
< span class = "reserved" > return< / span > < span class = "plain" > < / span > < span class = "identifier" > I< / span > < span class = "plain" > ?(< / span > < span class = "identifier" > I< / span > < span class = "plain" > -> < / span > < span class = "element" > item_contents< / span > < span class = "plain" > ):< / span > < span class = "identifier" > NULL< / span > < span class = "plain" > ;< / span >
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< span class = "plain" > }< / span >
< / pre >
< p class = "inwebparagraph" > < / p >
< p class = "endnote" > The function LinkedLists::len is used in < a href = "#SP10" > § 10< / a > , 5/ee (< a href = "5-ee.html#SP7_3" > § 7.3< / a > ).< / p >
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< p class = "endnote" > The function LinkedLists::first is used in < a href = "#SP7" > § 7< / a > , 7/vn (< a href = "7-vn.html#SP8" > § 8< / a > ).< / p >
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< p class = "endnote" > The function LinkedLists::entry is used in < a href = "#SP7" > § 7< / a > .< / p >
< p class = "endnote" > The function LinkedLists::last is used in < a href = "#SP7" > § 7< / a > .< / p >
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< p class = "endnote" > The function LinkedLists::next is used in < a href = "#SP7" > § 7< / a > , 7/vn (< a href = "7-vn.html#SP8" > § 8< / a > ).< / p >
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< p class = "endnote" > The function LinkedLists::content is used in < a href = "#SP7" > § 7< / a > , 7/vn (< a href = "7-vn.html#SP8" > § 8< / a > ).< / p >
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< p class = "inwebparagraph" > < a id = "SP7" > < / a > < b > § 7. A macro-ized API. < / b > These intentionally hide the implementation. The difference between
< code class = "display" > < span class = "extract" > FIRST_IN_LINKED_LIST< / span > < / code > and < code class = "display" > < span class = "extract" > FIRST_ITEM_IN_LINKED_LIST< / span > < / code > is that one returns
the first structure in the list, and the other returns the first
< code class = "display" > < span class = "extract" > linked_list_item< / span > < / code > chunk in the list. From the latter you can make the
former using < code class = "display" > < span class = "extract" > CONTENT_IN_ITEM< / span > < / code > , but not vice versa. The same object
may be listed in many different lists, so if all you have is the object,
you don't know its place in the list.
< / p >
< pre class = "definitions" >
< span class = "definitionkeyword" > define< / span > < span class = "identifier" > NEW_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::new< / span > < span class = "plain" > ())< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > FIRST_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::first< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > ENTRY_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) (< / span > < span class = "functiontext" > LinkedLists::entry< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > DELETE_FROM_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) (< / span > < span class = "functiontext" > LinkedLists::delete< / span > < span class = "plain" > (< / span > < span class = "identifier" > N< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > LAST_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::last< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > NEXT_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::next< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > ))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > CONTENT_IN_ITEM< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) (< / span > < span class = "functiontext" > LinkedLists::content< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > )))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > ADD_TO_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "functiontext" > LinkedLists::add< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > , (< / span > < span class = "reserved" > void< / span > < span class = "plain" > *) (< / span > < span class = "identifier" > I< / span > < span class = "plain" > ), < / span > < span class = "constant" > TRUE< / span > < span class = "plain" > )< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > FIRST_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) (< / span > < span class = "functiontext" > LinkedLists::content< / span > < span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::first< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > LAST_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) (< / span > < span class = "functiontext" > LinkedLists::content< / span > < span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::last< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))))< / span >
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< / pre >
< p class = "inwebparagraph" > < a id = "SP8" > < / a > < b > § 8. < / b > The following macro requires slight care to use: the list < code class = "display" > < span class = "extract" > L< / span > < / code > needs to be
calculable without side-effects. There's no such worry over < code class = "display" > < span class = "extract" > P< / span > < / code > or < code class = "display" > < span class = "extract" > T< / span > < / code > , since
they're just identifier names: the loop variable and the type name respectively.
< / p >
< p class = "inwebparagraph" > Note that the loop variable < code class = "display" > < span class = "extract" > P< / span > < / code > must already be defined. Inside the loop body,
a new variable will also then exist, < code class = "display" > < span class = "extract" > P_item< / span > < / code > , to refer to the item which
points to < code class = "display" > < span class = "extract" > P< / span > < / code > . This allows us to iterate despite the comments above.
< / p >
< pre class = "definitions" >
< span class = "definitionkeyword" > define< / span > < span class = "identifier" > LOOP_OVER_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > P< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "reserved" > for< / span > < span class = "plain" > (< / span > < span class = "reserved" > linked_list_item< / span > < span class = "plain" > *< / span > < span class = "identifier" > P< / span > < span class = "plain" > ##< / span > < span class = "identifier" > _item< / span > < span class = "plain" > = (< / span > < span class = "identifier" > P< / span > < span class = "plain" > = < / span > < span class = "identifier" > FIRST_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > ), < / span > < span class = "identifier" > FIRST_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > ));< / span >
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< span class = "identifier" > P< / span > < span class = "plain" > ##< / span > < span class = "identifier" > _item< / span > < span class = "plain" > ;< / span >
< span class = "identifier" > P< / span > < span class = "plain" > ##< / span > < span class = "identifier" > _item< / span > < span class = "plain" > = (< / span > < span class = "identifier" > P< / span > < span class = "plain" > = < / span > < span class = "identifier" > CONTENT_IN_ITEM< / span > < span class = "plain" > (< / span > < span class = "identifier" > NEXT_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > P< / span > < span class = "plain" > ##< / span > < span class = "identifier" > _item< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > ), < / span > < span class = "identifier" > T< / span > < span class = "plain" > ), < / span > < span class = "identifier" > NEXT_ITEM_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > P< / span > < span class = "plain" > ##< / span > < span class = "identifier" > _item< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > )))< / span >
< / pre >
< p class = "inwebparagraph" > < a id = "SP9" > < / a > < b > § 9. LIFO stacks. < / b > The above gives us an almost free implementation of LIFO, last-in-first-out,
stacks, where we represent a stack as a linked list whose first entry is at
the front. To push an item, we add it at the front; to pull, we remove the
front iten.
< / p >
< p class = "inwebparagraph" > We provide an abstract type name for these stacks, even though they're the
exact same structure. For reasons to do with the way < code class = "display" > < span class = "extract" > typedef< / span > < / code > works in C,
it is awkward to typedef the two names together, so we'll simply use the
preprocessor:
< / p >
< pre class = "definitions" >
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< span class = "definitionkeyword" > define< / span > < span class = "constant" > lifo_stack< / span > < span class = "plain" > < / span > < span class = "reserved" > linked_list< / span >
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< / pre >
< p class = "inwebparagraph" > < a id = "SP10" > < / a > < b > § 10. < / b > Otherwise, it's macros all the way:
< / p >
< pre class = "definitions" >
< span class = "definitionkeyword" > define< / span > < span class = "identifier" > NEW_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::new< / span > < span class = "plain" > ())< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > PUSH_TO_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > I< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "functiontext" > LinkedLists::add< / span > < span class = "plain" > ((< / span > < span class = "identifier" > L< / span > < span class = "plain" > ), (< / span > < span class = "reserved" > void< / span > < span class = "plain" > *) (< / span > < span class = "identifier" > I< / span > < span class = "plain" > ), < / span > < span class = "constant" > FALSE< / span > < span class = "plain" > )< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > PULL_FROM_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "identifier" > T< / span > < span class = "plain" > *) < / span > < span class = "functiontext" > LinkedLists::remove_from_front< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > POP_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > (< / span > < span class = "functiontext" > LinkedLists::remove_from_front< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ))< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > TOP_OF_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
< span class = "identifier" > FIRST_IN_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
< span class = "definitionkeyword" > define< / span > < span class = "identifier" > LIFO_STACK_EMPTY< / span > < span class = "plain" > (< / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
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< span class = "plain" > ((< / span > < span class = "functiontext" > LinkedLists::len< / span > < span class = "plain" > (< / span > < span class = "identifier" > L< / span > < span class = "plain" > ) == < / span > < span class = "constant" > 0< / span > < span class = "plain" > )?< / span > < span class = "identifier" > TRUE:FALSE< / span > < span class = "plain" > )< / span >
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< span class = "definitionkeyword" > define< / span > < span class = "identifier" > LOOP_DOWN_LIFO_STACK< / span > < span class = "plain" > (< / span > < span class = "identifier" > P< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
< span class = "identifier" > LOOP_OVER_LINKED_LIST< / span > < span class = "plain" > (< / span > < span class = "identifier" > P< / span > < span class = "plain" > , < / span > < span class = "identifier" > T< / span > < span class = "plain" > , < / span > < span class = "identifier" > L< / span > < span class = "plain" > )< / span >
< / pre >
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< hr class = "tocbar" >
< ul class = "toc" > < li > < a href = "2-mth.html" > Back to 'Methods'< / a > < / li > < li > < a href = "2-dct.html" > Continue with 'Dictionaries'< / a > < / li > < / ul > < hr class = "tocbar" >
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<!-- End of weave -->
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< / main >
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< / body >
< / html >
