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sysconf
We recommend that you first test for a macro definition for the
parameter you are interested in, and call sysconf
only if the
macro is not defined. For example, here is how to test whether job
control is supported:
int have_job_control (void) { #ifdef _POSIX_JOB_CONTROL return 1; #else int value = sysconf (_SC_JOB_CONTROL); if (value < 0) /* If the system is that badly wedged, there’s no use trying to go on. */ fatal (strerror (errno)); return value; #endif }
Here is how to get the value of a numeric limit:
int get_child_max () { #ifdef CHILD_MAX return CHILD_MAX; #else int value = sysconf (_SC_CHILD_MAX); if (value < 0) fatal (strerror (errno)); return value; #endif }