ffs man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

ffs — find first set bit


#include <strings.h>

int ffs(int i);


The ffs() function shall find the first bit set (beginning with the least significant bit) in i, and return the index of that bit. Bits are numbered starting at one (the least significant bit).

Return Value

The ffs() function shall return the index of the first bit set. If i is 0, then ffs() shall return 0.


No errors are defined.

The following sections are informative.

See Also

The Base Definitions volume of POSIX.1‐2008, <strings.h>


2013 IEEE/The Open Group POSIX Programmer's Manual