int usleep(useconds_t usec);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.12:
(_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
!(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
The usleep() function suspends execution of the calling thread for (at
least) usec microseconds. The sleep may be lengthened slightly by any
system activity or by the time spent processing the call or by the
granularity of system timers.
0 on success, -1 on error.
EINTR Interrupted by a signal; see signal(7).
EINVAL usec is not smaller than 1000000. (On systems where that is
considered an error.)
4.3BSD, POSIX.1-2001. POSIX.1-2001 declares this function obsolete;
use nanosleep(2) instead. POSIX.1-2008 removes the specification of
On the original BSD implementation, and in glibc before version 2.2.2,
the return type of this function is void. The POSIX version returns
int, and this is also the prototype used since glibc 2.2.2.
Only the EINVAL error return is documented by SUSv2 and POSIX.1-2001.
The type useconds_t is an unsigned integer type capable of holding
integers in the range [0,1000000]. Programs will be more portable if
they never mention this type explicitly. Use
unsigned int usecs;
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
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