Difference between revisions of "LlGetListLength"
Omei Qunhua (talk | contribs) m (Removed a poorly written caveat that wasn't a caveat and is covered elsewhere on the page. Added info on bytecode space comparison.) |
Omei Qunhua (talk | contribs) (clean up) |
||
| Line 32: | Line 32: | ||
while (index < length) | while (index < length) | ||
{ | { | ||
llSay(0, llList2String(mylist, index)); | |||
llSay( | |||
++index; | ++index; | ||
} | } | ||
| Line 45: | Line 43: | ||
while (index < llGetListLength(mylist)) | while (index < llGetListLength(mylist)) | ||
{ | { | ||
llSay(0, llList2String(mylist, index)); | |||
llSay( | |||
++index; | ++index; | ||
} | } | ||
| Line 53: | Line 49: | ||
===LSO Optimizations=== | ===LSO Optimizations=== | ||
A faster and lighter (in bytecode) way to determine the length of a list is to do a not-equals compare with a null list. This works because the list not-equals compare returns the difference between the lengths, meaning that it returns the same result as <code>llGetListLength()</code>, minus the overhead in bytecode, and performance penalty of calling a non-native function. Note: This optimization is much less beneficial in Mono | A faster and lighter (in bytecode) way to determine the length of a list is to do a not-equals compare with a null list. This works because the list not-equals compare returns the difference between the lengths, meaning that it returns the same result as <code>llGetListLength()</code>, minus the overhead in bytecode, and performance penalty of calling a non-native function. Note: This optimization is much less beneficial time-wise in Mono as Mono's llGetListLength function is almost twice as fast, however the bytecode saving is still about 30 bytes. | ||
<lsl> | <lsl> | ||
list in; | list in; | ||
Revision as of 05:53, 4 January 2013
| LSL Portal | Functions | Events | Types | Operators | Constants | Flow Control | Script Library | Categorized Library | Tutorials |
Summary
Function: integer llGetListLength( list src );| 0.0 | Forced Delay |
| 10.0 | Energy |
Returns an integer that is the number of elements in the list src.
| • list | src |
Examples
<lsl> //Basic usage default {
state_entry()
{
list testList = ["one", "two", "three"];
integer length = llGetListLength(testList);
llOwnerSay("There are " + (string)length + " entries in the list.");
}
}
</lsl>Notes
Best Practices
When using list length to help you loop through a list, it is better to determine the length first, then start your loop:
<lsl> integer length = llGetListLength(mylist);
integer index;// default is 0 while (index < length) {
llSay(0, llList2String(mylist, index)); ++index;
} </lsl>
The following example is to illustrate what not to do, it calculates the length in the "for" loop and is inefficient because the length gets recalculated at each pass through the loop. This should only ever be done if the list is in fact changing (in length) with each iteration of the loop[1].
<lsl> integer index;// default is 0 while (index < llGetListLength(mylist)) {
llSay(0, llList2String(mylist, index)); ++index;
} </lsl>
LSO Optimizations
A faster and lighter (in bytecode) way to determine the length of a list is to do a not-equals compare with a null list. This works because the list not-equals compare returns the difference between the lengths, meaning that it returns the same result as llGetListLength(), minus the overhead in bytecode, and performance penalty of calling a non-native function. Note: This optimization is much less beneficial time-wise in Mono as Mono's llGetListLength function is almost twice as fast, however the bytecode saving is still about 30 bytes.
<lsl>
list in;
integer len_in = llGetListLength(in);
integer flen_in = (in != []);
//flen_in and len_in will be the same
integer neg_len_in = -llGetListLength(in); integer fneg_len_in = ([] != in); //fneg_len_in and neg_len_in will be the same </lsl>
See Also
Functions
| • | llListStatistics | – | LIST_STAT_NUM_COUNT – Returns the number of integers and floats in the list | |
| • | llStringLength | – | Returns the number of characters in a string. |
Deep Notes
Source
'linden\indra\lscript\lscript_library\lscript_alloc.cpp' @ lsa_cmp_lists
'linden\indra\lscript\lscript_execute\lscript_execute.cpp' @ list_list_operation
Footnotes
- ^ Recalculating the length is slow because the VM duplicates the entire list (including the values) when it is pushed on the stack (so it can be popped off the stack when the length is calculated).
Signature |
|---|
function integer llGetListLength( list src ); |