1MALLOC(3) Linux Programmer's Manual MALLOC(3)
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6 malloc, free, calloc, realloc - allocate and free dynamic memory
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9 #include <stdlib.h>
10 void *malloc(size_t size);
12 void free(void *ptr);
13 void *calloc(size_t nmemb, size_t size);
14 void *realloc(void *ptr, size_t size);
15 void *reallocarray(void *ptr, size_t nmemb, size_t size);
16 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
18 reallocarray():
20 _GNU_SOURCE
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23 The malloc() function allocates size bytes and returns a pointer to the
24 allocated memory. The memory is not initialized. If size is 0, then
25 malloc() returns either NULL, or a unique pointer value that can later
26 be successfully passed to free().
27 The free() function frees the memory space pointed to by ptr, which
29 must have been returned by a previous call to malloc(), calloc(), or
30 realloc(). Otherwise, or if free(ptr) has already been called before,
31 undefined behavior occurs. If ptr is NULL, no operation is performed.
32 The calloc() function allocates memory for an array of nmemb elements
34 of size bytes each and returns a pointer to the allocated memory. The
35 memory is set to zero. If nmemb or size is 0, then calloc() returns
36 either NULL, or a unique pointer value that can later be successfully
37 passed to free().
38 The realloc() function changes the size of the memory block pointed to
40 by ptr to size bytes. The contents will be unchanged in the range from
41 the start of the region up to the minimum of the old and new sizes. If
42 the new size is larger than the old size, the added memory will not be
43 initialized. If ptr is NULL, then the call is equivalent to mal‐
44 loc(size), for all values of size; if size is equal to zero, and ptr is
45 not NULL, then the call is equivalent to free(ptr). Unless ptr is
46 NULL, it must have been returned by an earlier call to malloc(), cal‐
47 loc(), or realloc(). If the area pointed to was moved, a free(ptr) is
48 done.
49 The reallocarray() function changes the size of the memory block
51 pointed to by ptr to be large enough for an array of nmemb elements,
52 each of which is size bytes. It is equivalent to the call
53 realloc(ptr, nmemb * size);
55 However, unlike that realloc() call, reallocarray() fails safely in the
57 case where the multiplication would overflow. If such an overflow
58 occurs, reallocarray() returns NULL, sets errno to ENOMEM, and leaves
59 the original block of memory unchanged.
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62 The malloc() and calloc() functions return a pointer to the allocated
63 memory, which is suitably aligned for any built-in type. On error,
64 these functions return NULL. NULL may also be returned by a successful
65 call to malloc() with a size of zero, or by a successful call to cal‐
66 loc() with nmemb or size equal to zero.
67 The free() function returns no value.
69 The realloc() function returns a pointer to the newly allocated memory,
71 which is suitably aligned for any built-in type and may be different