malloc
Allocates memory blocks.
void *malloc(
size_t size
);
size
Bytes to allocate.
malloc
returns a void pointer to the allocated space, or NULL
if there's insufficient memory available. To return a pointer to a type other than void
, use a type cast on the return value. The storage space pointed to by the return value is suitably aligned for storage of any type of object that has an alignment requirement less than or equal to that of the fundamental alignment. (In Visual C++, the fundamental alignment is the alignment that's required for a double
, or 8 bytes. In code that targets 64-bit platforms, it's 16 bytes.) Use _aligned_malloc
to allocate storage for objects that have a larger alignment requirement—for example, the SSE types __m128
and __m256
, and types that are declared by using __declspec(align( n ))
where n
is greater than 8. If size
is 0, malloc
allocates a zero-length item in the heap and returns a valid pointer to that item. Always check the return from malloc
, even if the amount of memory requested is small.
The malloc
function allocates a memory block of at least size
bytes. The block may be larger than size
bytes because of the space that's required for alignment and maintenance information.
malloc
sets errno
to ENOMEM
if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ
. For information about this and other error codes, see errno
, _doserrno
, _sys_errlist
, and _sys_nerr
.
The startup code uses malloc
to allocate storage for the _environ
, envp
, and argv
variables. The following functions and their wide-character counterparts also call malloc
.
The C++ _set_new_mode
function sets the new handler mode for malloc
. The new handler mode indicates whether, on failure, malloc
is to call the new handler routine as set by _set_new_handler
. By default, malloc
doesn't call the new handler routine on failure to allocate memory. You can override this default behavior so that, when malloc
fails to allocate memory, malloc
calls the new handler routine in the same way that the new
operator does when it fails for the same reason. To override the default, call _set_new_mode(1)
early in your program, or link with NEWMODE.OBJ
(see Link options).
When the application is linked with a debug version of the C run-time libraries, malloc
resolves to _malloc_dbg
. For more information about how the heap is managed during the debugging process, see CRT debug heap details.
malloc
is marked __declspec(noalias)
and __declspec(restrict)
. These attributes mean that the function is guaranteed not to modify global variables, and that the pointer returned isn't aliased. For more information, see noalias
and restrict
.
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Routine | Required header |
---|---|
malloc |
<stdlib.h> and <malloc.h> |
For more compatibility information, see Compatibility.
All versions of the C run-time libraries.
// crt_malloc.c
// This program allocates memory with
// malloc, then frees the memory with free.
#include <stdlib.h> // For _MAX_PATH definition
#include <stdio.h>
#include <malloc.h>
int main( void )
{
char *string;
// Allocate space for a path name
string = malloc( _MAX_PATH );
// In a C++ file, explicitly cast malloc's return. For example,
// string = (char *)malloc( _MAX_PATH );
if( string == NULL )
printf( "Insufficient memory available\n" );
else
{
printf( "Memory space allocated for path name\n" );
free( string );
printf( "Memory freed\n" );
}
}
Memory space allocated for path name
Memory freed