Difference between revisions of "Goto"
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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. | 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. | ||
| − | As an example, here an excerpt from | + | As an example, here an excerpt from FPC’s code base {{gitlab|blob|FPC|release_3_2_0/rtl/inc/extres.inc#L324-376|<tt>rtl/inc/extres.inc</tt>}}]: |
<syntaxhighlight lang="pascal" line start="324">procedure InitResources;</syntaxhighlight> | <syntaxhighlight lang="pascal" line start="324">procedure InitResources;</syntaxhighlight> | ||
<syntaxhighlight lang="pascal" line start="328" highlight="1">label ExitErrMem, ExitErrFile, ExitNoErr; | <syntaxhighlight lang="pascal" line start="328" highlight="1">label ExitErrMem, ExitErrFile, ExitNoErr; | ||
Revision as of 16:38, 23 January 2022
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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.
