1MALLOC(3) Linux Programmer's Manual MALLOC(3)
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6 malloc, free, calloc, realloc, reallocarray - allocate and free dynamic
7 memory
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10 #include <stdlib.h>
11 void *malloc(size_t size);
13 void free(void *ptr);
14 void *calloc(size_t nmemb, size_t size);
15 void *realloc(void *ptr, size_t size);
16 void *reallocarray(void *ptr, size_t nmemb, size_t size);
17 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
19 reallocarray():
21 Since glibc 2.29:
22 _DEFAULT_SOURCE
23 Glibc 2.28 and earlier:
24 _GNU_SOURCE
25
27 The malloc() function allocates size bytes and returns a pointer to the
28 allocated memory. The memory is not initialized. If size is 0, then
29 malloc() returns either NULL, or a unique pointer value that can later
30 be successfully passed to free().
31 The free() function frees the memory space pointed to by ptr, which
33 must have been returned by a previous call to malloc(), calloc(), or
34 realloc(). Otherwise, or if free(ptr) has already been called before,
35 undefined behavior occurs. If ptr is NULL, no operation is performed.
36 The calloc() function allocates memory for an array of nmemb elements
38 of size bytes each and returns a pointer to the allocated memory. The
39 memory is set to zero. If nmemb or size is 0, then calloc() returns
40 either NULL, or a unique pointer value that can later be successfully
41 passed to free(). If the multiplication of nmemb and size would result
42 in integer overflow, then calloc() returns an error. By contrast, an
43 integer overflow would not be detected in the following call to mal‐
44 loc(), with the result that an incorrectly sized block of memory would
45 be allocated:
46 malloc(nmemb * size);
48 The realloc() function changes the size of the memory block pointed to
50 by ptr to size bytes. The contents will be unchanged in the range from
51 the start of the region up to the minimum of the old and new sizes. If
52 the new size is larger than the old size, the added memory will not be
53 initialized. If ptr is NULL, then the call is equivalent to mal‐
54 loc(size), for all values of size; if size is equal to zero, and ptr is
55 not NULL, then the call is equivalent to free(ptr) (this behavior is
56 nonportable; see NOTES). Unless ptr is NULL, it must have been re‐
57 turned by an earlier call to malloc(), calloc(), or realloc(). If the
58 area pointed to was moved, a free(ptr) is done.
59 The reallocarray() function changes the size of the memory block
61 pointed to by ptr to be large enough for an array of nmemb elements,
62 each of which is size bytes. It is equivalent to the call
63 realloc(ptr, nmemb * size);
65 However, unlike that realloc() call, reallocarray() fails safely in the
67 case where the multiplication would overflow. If such an overflow oc‐
68 curs, reallocarray() returns NULL, sets