Is a malloc() needed before a realloc()?

c memory-management malloc alloc
j riv picture j riv · Dec 16, 2010 · Viewed 18.9k times · Source

Since I had read realloc will act as malloc if the size pointed is 0, I was using it without malloc(), provided the pointer was static, global, or explicitly set to NULL if automatic.

However, I notice a lot of programmers try to set it or set it to malloc(1). Is it needed?

Answer

Simone picture Simone · Dec 16, 2010

From Open Groups' specifications:

If ptr is a null pointer, realloc() shall be equivalent to malloc() for the specified size.

If ptr does not match a pointer returned earlier by calloc(), malloc(), or realloc() or if the space has previously been deallocated by a call to free() or realloc(), the behavior is undefined.

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