malloc
<stdlib.h>
Allocates size
bytes of uninitialized storage.
If allocation succeeds, returns a pointer that is suitably aligned for any object type with fundamental alignment.
If size
is zero, the behavior of malloc
is implementation-defined. For example, a null pointer may be returned. Alternatively, a non-null pointer may be returned; but such a pointer should not be dereferenced, and should be passed to free to avoid memory leaks.
malloc
is thread-safe: it behaves as though only accessing the memory locations visible through its argument, and not any static storage.
A previous call to free , free_sized, and free_aligned_sized(since C23) or realloc that deallocates a region of memory synchronizes-with a call to malloc
that allocates the same or a part of the same region of memory. This synchronization occurs after any access to the memory by the deallocating function and before any access to the memory by malloc
. There is a single total order of all allocation and deallocation functions operating on each particular region of memory.
[edit] Parameters
[edit] Return value
On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated with free() or realloc() .
On failure, returns a null pointer.
[edit] Example
#include <stdio.h> #include <stdlib.h> int main(void) { int *p1 = malloc(4*sizeof(int)); // allocates enough for an array of 4 int int *p2 = malloc(sizeof(int[4])); // same, naming the type directly int *p3 = malloc(4*sizeof *p3); // same, without repeating the type name if(p1) { for(int n=0; n<4; ++n) // populate the array p1[n] = n*n; for(int n=0; n<4; ++n) // print it back out printf ("p1[%d] == %d\n", n, p1[n]); } free (p1); free (p2); free (p3); }
Output:
p1[0] == 0 p1[1] == 1 p1[2] == 4 p1[3] == 9
[edit] References
- C17 standard (ISO/IEC 9899:2018):
- 7.22.3.4 The malloc function (p: 254)
- C11 standard (ISO/IEC 9899:2011):
- 7.22.3.4 The malloc function (p: 349)
- C99 standard (ISO/IEC 9899:1999):
- 7.20.3.3 The malloc function (p: 314)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.10.3.3 The malloc function