malloc(3x)
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malloc, free, realloc, calloc, mallopt, mallinfo Subroutine
fast main memory allocator
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SYNTAX
#include <malloc.h>
char *malloc (size)
unsigned size;
void free (ptr)
char *ptr;
char *realloc (ptr, size)
char *ptr;
unsigned size;
char *calloc (nelem, elsize)
unsigned nelem, elsize;
int mallopt (cmd, value)
int cmd, value;
struct mallinfo mallinfo()
DESCRIPTION
Malloc and free provide a simple general-purpose memory
allocation package that runs considerably faster than the
malloc(3C) package. It is found in the library malloc, and is
loaded if the option -lmalloc is used with cc(1) or ld(1).
Malloc returns a pointer to a block of at least size bytes
suitably aligned for any use.
The argument to free is a pointer to a block previously allocated
by malloc; after free is performed, this space is made available
for further allocation, and its contents destroyed (see mallopt
below for a way to change this behavior).
Undefined results will occur if the space assigned by malloc is
overrun or if some random number is handed to free.
Realloc changes the size of the block pointed to by ptr to size
bytes and returns a pointer to the (possibly moved) block. The
contents will be unchanged up to the lesser of the new and old
sizes.
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malloc(3x)
Calloc allocates space for an array of nelem elements of size
elsize. The space is initialized to zeros.
Mallopt lets you control the allocation algorithm. The available
values for cmd are:
M_MXFAST Set maxfast to value. The algorithm allocates all
blocks below the size of maxfast in large groups and
then doles them out very quickly. The default value for
maxfast is 0.
M_NLBLKS Set numlblks to value. The above-mentioned large groups
each contain numlblks blocks. Numlblks must be greater
than 0. The default value for numlblks is 100.
M_GRAIN Set grain to value. The sizes of all blocks smaller
than maxfast are considered to be rounded up to the
nearest multiple of grain. Grain must be greater than
0. The default value of grain is the smallest number of
bytes that will allow alignment of any data type. Value
will be rounded up to a multiple of the default when
grain is set.
M_KEEP Preserve data in a freed block until the next malloc,
realloc, or calloc. This option is provided only for
compatibility with the old version of malloc and is not
recommended.
These values are defined in the <malloc.h> header file.
Mallopt may be called repeatedly, but it may not be called after
the first small block is allocated.
Mallinfo returns information about space usage. It returns the
structure:
struct mallinfo {
int arena; /* total space in arena */
int ordblks; /* number of ordinary blocks */
int smblks; /* number of small blocks */
int hblkhd; /* space in holding block headers */
int hblks; /* number of holding blocks */
int usmblks; /* space in small blocks in use */
int fsmblks; /* space in free small blocks */
int uordblks; /* space in ordinary blocks in use */
int fordblks; /* space in free ordinary blocks */
int keepcost; /* space penalty if keep option */
/* is used */
}
This structure is defined in the <malloc.h> header file.
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malloc(3x)
Each of the allocation routines returns a pointer to space
suitably aligned (after possible pointer coercion) for storage of
any type of object.
SEE ALSO
brk(2), malloc(3C).
DIAGNOSTICS
Malloc, realloc and calloc return a NULL pointer if there is not
enough available memory. When realloc returns NULL, the block
pointed to by ptr is left intact. If mallopt is called after any
allocation or if cmd or value are invalid, non-zero is returned.
Otherwise, it returns zero.
WARNINGS
This package usually uses more data space than malloc(3C).
The code size is also bigger than malloc(3C).
Note that unlike malloc(3C), this package does not preserve the
contents of a block when it is freed, unless the M_KEEP option of
mallopt is used.
Undocumented features of malloc(3C) have not been duplicated.
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