brk, sbrk - 改变数据段大小
int brk(void *end_data_segment); void *sbrk(intptr_t increment);
brk() 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.
On success, brk() returns zero, and sbrk() returns a pointer to the start of the new area. On error, -1 is returned, and errno is set to ENOMEM.
遵循于4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
brk() and sbrk() are not defined in the C Standard and are deliberately excluded from the POSIX.1 standard (see paragraphs B.220.127.116.11 and B.8.3.3).
Various systems use various types for the parameter of sbrk(). Common are int, ssize_t,ptrdiff_t, intptr_t.
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