Goto
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Revision as of 16:20, 14 October 2018 by Kai Burghardt (talk | contribs) (→see also: mention system.longJmp)
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goto
is an unconditional jump to a previously declared label
(either before or after the goto
command).
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 is 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.