Difference between revisions of "Goto"
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The last situation a <syntaxhighlight enclose="none" lang="pascal">goto</syntaxhighlight> is agreed with bad grace is a significant system error, where a “graceful exit” is better than causing a system breakdown. | The last situation a <syntaxhighlight enclose="none" lang="pascal">goto</syntaxhighlight> 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 [https://svn.freepascal.org/cgi-bin/viewvc.cgi/tags/release_3_0_4/rtl/inc/extres.inc?revision=37113&view=markup <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>]: |
<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="328">label ExitErrMem, ExitErrFile, ExitNoErr; | <syntaxhighlight lang="pascal" line start="328" highlight="328">label ExitErrMem, ExitErrFile, ExitNoErr; |
Revision as of 18:51, 7 March 2018
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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.