BRKSection: Linux Programmer's Manual (2)
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NAMEbrk, sbrk - change data segment size
int brk(void *end_data_segment);
DESCRIPTIONbrk() sets the end of the data segment to the value specified by end_data_segment, when that value is reasonable, the system does have enough memory and the process does not exceed its max data size (see setrlimit(2)).
sbrk() increments the program's data space by increment bytes. sbrk() isn't a system call, it is just a C library wrapper. Calling sbrk() with an increment of 0 can be used to find the current location of the program break.
RETURN VALUEOn success, brk() returns zero. On error, -1 is returned, and errno is set to ENOMEM. (But see Linux Notes below.)
CONFORMING TO4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
NOTESVarious systems use various types for the parameter of sbrk(). Common are int, ssize_t, ptrdiff_t, intptr_t.
Linux NotesThe return value described above for brk() is the behaviour provided by the glibc wrapper function for the Linux brk() system call. (On most other implementations, the return value from brk() is the same.) However, the actual Linux system call returns the new program break on success. On failure, the system call returns the current break (thus for example, the call brk(0) can be used to obtain the current break). The glibc wrapper function does some work to provide the 0 and -1 return values described above.
SEE ALSOexecve(2), getrlimit(2), malloc(3)