Examples of good gotos in C or C++

Asked 2008-10-29T03:58:30.967

In this thread, we look at examples of good uses of goto in C or C++. It's inspired by an answer which people voted up because they thought I was joking.

Summary (label changed from original to make intent even clearer):

infinite_loop:

    // code goes here

goto infinite_loop;

Why it's better than the alternatives:

It's specific. goto is the language construct which causes an unconditional branch. Alternatives depend on using structures supporting conditional branches, with a degenerate always-true condition.
The label documents the intent without extra comments.
The reader doesn't have to scan the intervening code for early breaks (although it's still possible for an unprincipled hacker to simulate continue with an early goto).

Rules:

Pretend that the gotophobes didn't win. It's understood that the above can't be used in real code because it goes against established idiom.
Assume that we have all heard of 'Goto considered harmful' and know that goto can be used to write spaghetti code.
If you disagree with an example, criticize it on technical merit alone ('Because people don't like goto' is not a technical reason).

Let's see if we can talk about this like grown ups.

Edit

This question seems finished now. It generated some high quality answers. Thanks to everyone, especially those who took my little loop example seriously. Most skeptics were concerned by the lack of block scope. As @quinmars pointed out in a comment, you can always put braces around the loop body. I note in passing that for(;;) and while(true) don't give you the braces for free either (and omitting

c++ c goto

Edit Report

2 Answers

Very common.

do_stuff(thingy) {
    lock(thingy);

    foo;
    if (foo failed) {
        status = -EFOO;
        goto OUT;
    }

    bar;
    if (bar failed) {
        status = -EBAR;
        goto OUT;
    }

    do_stuff_to(thingy);

OUT:
    unlock(thingy);
    return status;
}

The only case I ever use goto is for jumping forwards, usually out of blocks, and never into blocks. This avoids abuse of do{}while(0) and other constructs which increase nesting, while still maintaining readable, structured code.

answered 2008-10-29T04:18:02.097

One good place to use a goto is in a procedure that can abort at several points, each of which requires various levels of cleanup. Gotophobes can always replace the gotos with structured code and a series of tests, but I think this is more straightforward because it eliminates excessive indentation:

if (!openDataFile())
  goto quit;

if (!getDataFromFile())
  goto closeFileAndQuit;

if (!allocateSomeResources)
  goto freeResourcesAndQuit;

// Do more work here....

freeResourcesAndQuit:
   // free resources
closeFileAndQuit:
   // close file
quit:
   // quit!

answered 2008-10-29T04:09:17.607

Examples of good gotos in C or C++

2 Answers

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