2.25 mallinfo, malloc_stats, mallopt—malloc support

Synopsis

#include <malloc.h>
struct mallinfo mallinfo(void);
void malloc_stats(void);
int mallopt(int parameter, value);

struct mallinfo _mallinfo_r(void *reent);
void _malloc_stats_r(void *reent);
int _mallopt_r(void *reent, int parameter, value);

Description
mallinfo returns a structure describing the current state of memory allocation. The structure is defined in malloc.h. The following fields are defined: arena is the total amount of space in the heap; ordblks is the number of chunks which are not in use; uordblks is the total amount of space allocated by malloc; fordblks is the total amount of space not in use; keepcost is the size of the top most memory block.

malloc_stats print some statistics about memory allocation on standard error.

mallopt takes a parameter and a value. The parameters are defined in malloc.h, and may be one of the following: M_TRIM_THRESHOLD sets the maximum amount of unused space in the top most block before releasing it back to the system in free (the space is released by calling _sbrk_r with a negative argument); M_TOP_PAD is the amount of padding to allocate whenever _sbrk_r is called to allocate more space.

The alternate functions _mallinfo_r, _malloc_stats_r, and _mallopt_r are reentrant versions. The extra argument reent is a pointer to a reentrancy structure.

Returns
mallinfo returns a mallinfo structure. The structure is defined in malloc.h.

malloc_stats does not return a result.

mallopt returns zero if the parameter could not be set, or non-zero if it could be set.

Portability
mallinfo and mallopt are provided by SVR4, but mallopt takes different parameters on different systems. malloc_stats is not portable.