Difference between revisions of "Goto"
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{{goto}} | {{goto}} | ||
| + | <syntaxhighlight inline lang="pascal">goto</syntaxhighlight> is an unconditional jump to a previously declared [[Label|<syntaxhighlight inline lang="pascal">label</syntaxhighlight>]] (either before or after the <syntaxhighlight inline lang="pascal">goto</syntaxhighlight> command). | ||
| + | It is a [[Reserved words|reserved word]]. | ||
| − | + | Usage of <syntaxhighlight inline lang="pascal">goto</syntaxhighlight> in high-level programming languages such as Pascal is highly discredited, since control structures of all sorts are available. | |
| − | + | The last situation a <syntaxhighlight inline lang="pascal">goto</syntaxhighlight> is agreed with bad grace to be a significant system error, where a “graceful exit” is better than causing a system breakdown. | |
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| − | The last situation a <syntaxhighlight | ||
As an example, here an excerpt from FPC's code base [https://svn.freepascal.org/cgi-bin/viewvc.cgi/tags/release_3_0_4/rtl/inc/extres.inc?revision=37113&view=markup#l324 <tt>rtl/inc/extres.inc</tt>]: | As an example, here an excerpt from FPC's code base [https://svn.freepascal.org/cgi-bin/viewvc.cgi/tags/release_3_0_4/rtl/inc/extres.inc?revision=37113&view=markup#l324 <tt>rtl/inc/extres.inc</tt>]: | ||
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ExitNoErr: | ExitNoErr: | ||
end;</syntaxhighlight> | end;</syntaxhighlight> | ||
| − | According to the value of {{Doc|package=RTL|unit=system|identifier=returnnilifgrowheapfails|text=<syntaxhighlight | + | According to the value of {{Doc|package=RTL|unit=system|identifier=returnnilifgrowheapfails|text=<syntaxhighlight inline lang="pascal">returnNilIfGrowHeapFails</syntaxhighlight>}} {{Doc|package=RTL|unit=system|identifier=getmem|text=<syntaxhighlight inline lang="pascal">getMem</syntaxhighlight>}} possibly may return [[Nil|<syntaxhighlight inline lang="pascal">nil</syntaxhighlight>]]. |
| − | Instead of placing ''everything'' in a “success”-branch, a couple <syntaxhighlight | + | Instead of placing ''everything'' in a “success”-branch, a couple <syntaxhighlight inline lang="pascal">goto</syntaxhighlight> instructions were chosen. |
== See also == | == See also == | ||
| − | * [[sGoto|<syntaxhighlight lang="pascal" | + | * [[sGoto|<syntaxhighlight lang="pascal" inline>{$goto}</syntaxhighlight> compiler directive]] |
| − | * {{Doc|package=RTL|unit=system|identifier=longjmp|text=<syntaxhighlight lang="pascal" | + | * {{Doc|package=RTL|unit=system|identifier=longjmp|text=<syntaxhighlight lang="pascal" inline>system.longJmp</syntaxhighlight>}} |
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| + | [[Category: Code]] | ||
Revision as of 02:34, 6 May 2020
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goto is an unconditional jump to a previously declared label (either before or after the goto command).
It is a reserved word.
Usage of goto in high-level programming languages such as Pascal is highly discredited, since control structures of all sorts are available.
The last situation a goto is agreed with bad grace to be a significant system error, where a “graceful exit” is better than causing a system breakdown.
As an example, here an excerpt from FPC's code base rtl/inc/extres.inc:
324procedure InitResources;
328label ExitErrMem, ExitErrFile, ExitNoErr;
329begin
339 ResHeader:=GetMem(sizeof(TExtHeader));
340 if ResHeader=nil then goto ExitErrFile;
366 goto ExitNoErr;
367
368 ExitErrMem:
369 FreeMem(ResHeader);
370 ResHeader:=nil;
371 ExitErrFile:
372 {$I-}
373 Close(fd);
374 {$I+}
375 ExitNoErr:
376end;
According to the value of returnNilIfGrowHeapFails getMem possibly may return nil.
Instead of placing everything in a “success”-branch, a couple goto instructions were chosen.
