3 ms·
I guess it's fine to use multiple targets too. However, usually you can get away with one, because free(NULL) and similar cleanups tend to be no-ops. So you hav
by exDM69 15y ago
I guess it's fine to use multiple targets too. However, usually you can get away with one, because free(NULL) and similar cleanups tend to be no-ops. So you have something like:
char *foo = 0, *bar = 0;
if((foo = malloc(X)) == NULL || (bar = malloc(Y)) == NULL)
goto cleanup;
make_me_millions(foo, bar);
cleanup:
free(bar);
free(foo);
In this case, and many cases like it, there's no need to have two jump targets, because one is good enough. You'll have to declare the variables early on anyway to avoid warnings/errors from definitions that cross jump labels.
So there's probably nothing wrong with multiple jump targets but that might not be needed with well-behaving cleanup functions.
- adestefan 15y agobecause free(NULL) and similar cleanups tend to be no-ops. So you have something like You really need to check the specification on each function. free is defined that free(NULL) is no-op, but there are other things where that is not the case. Also, that code is not portable since NULL does not have to be 0.
- cdellin 15y agoJust a correction: the code is actually perfectly portable. The integer constant 0 is the canonical definition of the null pointer by definition in the standard (See Section 6.2.2.3 "Pointers" in C89). The null pointer constant (NULL) is defined primarily for convenience (so a reader knows you mean a null pointer instead of a arithmetic zero). Of course, the bitwise representation of the null pointer need not be all-bits-zero; that is, NULL = (void )0 != ((int *)&0).
- adestefan 15y agoI stand corrected, it does define the integer constant 0 to be promoted to the null pointer. In C11 this is Section 6.3.2.3. To make it even more confusing Section 7.19 Common Definitions <stddef.h> defines NULL to be an implementation depefined null pointer constant. I was always taught that (void *)0 is a valid definition of NULL, but that 0 was not necessarily.
- exDM69 15y ago> You really need to check the specification on each function. Sure, but I need to do that anyway and constantly, since I use far too many API's to memorize. It's also convenient to make cleanup(NULL) a no-op for the API's you create. NULL is zero. Even if the standard would allow it to be something else, it's not relevant with the compilers and platforms I use. There's no point in being a language lawyer just to achieve "portability" to some imaginary platform where a byte is 7 bits and NULL == 0xdeadbeef. Make a list of compilers and platforms you support and forget the rest if you want to get stuff done.