brk, sbrk - modify size of data segment

Syntax	#include <unistd.h> int brk(void *addr); void *sbrk(int incr);
Description	brk() and sbrk() are used for dynamic modification of the storage space allocated to the data segment of the calling process (cf. exec). The modification is made by resetting the space limit, or ’break value’, of the process and allocating a corresponding area. The break value is the first unoccupied address above the data segment. The extent of the allocated storage space increases as the break value is increased. Newly allocated storage space is set to zero, but if the same storage space is reallocated to the same process, its contents are undefined. brk() sets the break value to addr and modifies the allocated space accordingly. sbrk() adds incr bytes to the break value and modifies the allocated space accordingly. incr can be negative. In this case, the extent of the assigned storage space is reduced. The current break value is returned by sbrk(0). If an application also uses additional functions for storage space management, e.g. malloc(), mmap() or free(), the behavior of brk() and sbrk() is undefined. Other functions may use these other memory management functions silently. brk() and sbrk() are not reentrant.
Return val.	brk(): 0       if successful. -1      if an error occurs. errno is set to indicate the error.
	sbrk():
	previous break value
		if successful.
	(void*)-1	if an error occurs. errno is set to indicate the error.
Errors	brk() and sbrk() are unsuccessful and do not modify the allocated storage space if:
	ENOMEM	Such a modification would cause more space to be allocated than is allowed by the system-dependent maximum process size (see ulimit()).
Notes	The functions brk() and sbrk() used to be needed in special cases where no other memory management function would have offered the same possibilities. Now, however, the mmap() function is recommended, as it can be used simultaneously with all other memory management functions without problems. The pointer returned by sbrk() is not suitable for any other use.
See also	exec(), malloc(), mmap(), ulimit(), unistd.h.