Goto: what changed
Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.
Title: Goto
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| 1 | + | `goto` is an unconditional jump to a previously declared [[Label|label]] (either before or after the `goto` command). It is a [[Reserved words|reserved word]]. | |
| 2 | + | ||
| 3 | + | Usage of `goto` in high-level programming languages such as Pascal is highly discredited, since control structures of all sorts are available. | |
| 4 | + | ||
| 5 | + | 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. | |
| 6 | + | ||
| 7 | + | As an example, here an excerpt from FPC’s code base [`rtl/inc/extres.inc`](https://gitlab.com/freepascal.org/fpc/source/blob/release_3_2_0/rtl/inc/extres.inc#L324-376)\]: | |
| 8 | + | ||
| 9 | + | ``` pascal | |
| 10 | + | procedure InitResources; | |
| 11 | + | ``` | |
| 12 | + | ||
| 13 | + | ``` pascal | |
| 14 | + | label ExitErrMem, ExitErrFile, ExitNoErr; | |
| 15 | + | begin | |
| 16 | + | ``` | |
| 17 | + | ||
| 18 | + | ``` pascal | |
| 19 | + | ResHeader:=GetMem(sizeof(TExtHeader)); | |
| 20 | + | if ResHeader=nil then goto ExitErrFile; | |
| 21 | + | ``` | |
| 22 | + | ||
| 23 | + | ``` pascal | |
| 24 | + | goto ExitNoErr; | |
| 25 | + | ||
| 26 | + | ExitErrMem: | |
| 27 | + | FreeMem(ResHeader); | |
| 28 | + | ResHeader:=nil; | |
| 29 | + | ExitErrFile: | |
| 30 | + | {$I-} | |
| 31 | + | Close(fd); | |
| 32 | + | {$I+} | |
| 33 | + | ExitNoErr: | |
| 34 | + | end; | |
| 35 | + | ``` | |
| 36 | + | ||
| 37 | + | According to the value of [`returnNilIfGrowHeapFails`](https://www.freepascal.org/docs-html/rtl/system/returnnilifgrowheapfails.html) [`getMem`](https://www.freepascal.org/docs-html/rtl/system/getmem.html) possibly may return [[Nil|nil]]. Instead of placing *everything* in a “success”-branch, a couple `goto` instructions were chosen. | |
| 38 | + | ||
| 39 | + | ## See also | |
| 40 | + | ||
| 41 | + | - [[Exit|exit]] | |
| 42 | + | - [[sGoto|{$goto} compiler directive]] | |
| 43 | + | - [`system.longJmp`](https://www.freepascal.org/docs-html/rtl/system/longjmp.html) | |
| 44 | + | ||
| 45 | + | --- | |
| 46 | + | *From the Free Pascal wiki, page "Goto", as it stood on 2022-01-24 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).* | |
| 47 | + | Category: Code |