How detect malloc failure?

Question

What is the portable way to check whether malloc failed to allocate non-zero memory block?

Answer 1

malloc(n) returns NULL on failure.
malloc(0) may return NULL.

To detect failure:

void* ptr = malloc(n);
if (ptr == NULL && n > 0) Handle_Failure();

---

Notes:

As in OP's case: "... allocate non-zero memory block", often code is such that a 0 allocation request can not occur and so the 0 test is not needed.

size_t nstr = strlen(some_string) + 1;
void* ptrstr = malloc(nstr);
if (ptrstr == NULL) Handle_Failure();

Some systems set errno on failure, but not all. Setting errno due to memory allocation failure is not specified in the C11 spec.

malloc(n) expects n to be the unsigned type size_t. Using an int n with a negative value will certainly convert to some large unsigned value and then likely fail the memory allocation.