NAME

stdc_has_single_bit, stdc_has_single_bit_uc, stdc_has_single_bit_us, stdc_has_single_bit_ui, stdc_has_single_bit_ul, stdc_has_single_bit_ull — determine if only one bit is set

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdbit.h>

bool
stdc_has_single_bit(generic_value_type value);

bool
stdc_has_single_bit_uc(unsigned char value);

bool
stdc_has_single_bit_us(unsigned short value);

bool
stdc_has_single_bit_ui(unsigned int value);

bool
stdc_has_single_bit_ul(unsigned long value);

bool
stdc_has_single_bit_ull(unsigned long long value);

DESCRIPTION

The stdc_has_single_bit() family of functions determines whether the value has only a single bit set. value. The function returns true if there is exactly one bit whose value is set to one in value.

The stdc_has_single_bit() function is generic and will operate on all 8, 16, 32, and 64-bit unsigned integers; however, it is only available in C23. The other functions all operate on a specific integer type, but otherwise behave the same and are available regardless of the C language version.

RETURN VALUES

The functions in the stdc_has_single_bit() family return true if exactly one bit is set in value. Otherwise, false is returned. These functions cannot fail.

EXAMPLES

Example 1 Printing whether only a single bit is set.

#include <stdbit.h>
#include <stdio.h>
#include <limits.h>

int
main(void)
{
	printf("%s %s %s %s\n",
	    stdc_has_single_bit_uc(0x23) ? "true" : "false",
	    stdc_has_single_bit_us(0x0080) ? "true" : "false",
	    stdc_has_single_bit_ui(0x81941b23) ? "true" : "false",
	    stdc_has_single_bit_ull(0x00200000000000000) ?
	    "true" : "false");
	return (0);
}

When compiled and run, this produces:

$ ./a.out
false true false true

INTERFACE STABILITY

Committed

MT-LEVEL

Async-Signal-Safe