Compute the absolute value of a double number
Synopsis:
#include <math.h>
double fabs( double x );
float fabsf( float x );
long double fabsl( long double x );
Arguments:
 x
 The number you want the absolute value of.
Library:
 libm
 The generalpurpose math library.
 libmsve
 (QNX Neutrino 7.1 or later)
A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.
Your system requirements will determine how you should work with these libraries:
 If you want only selected processes to run with the SVE version, you can include both libraries in your OS image
and use the l m or l msve option to
qcc
to link explicitly against the appropriate one.
 If you want all processes to use the SVE version, include libmsve.so in your OS image
and set up a symbolic link from libm.so to libmsve.so.
Use the l m option to
qcc
to link against the library.
Note:
Compile your program with the fnobuiltin option to prevent the compiler from using a
builtin version of the function.
Description:
The fabs(), fabsf(), and fabsl()
functions compute the absolute value of x.
To check for error situations, use
feclearexcept()
and
fetestexcept().
For example:
 Call feclearexcept(FE_ALL_EXCEPT) before calling
fabs(), fabsf(), or fabsl().
 On return, if fetestexcept(FE_ALL_EXCEPT)
is nonzero, then an error has occurred.
Returns:
The absolute value of x.
If x is: 
These functions return: 
Errors: 
±0.0 
0.0 
— 
±Inf 
Inf 
— 
NaN 
NaN 
— 
These functions raise FE_INEXACT if the FPU reports that
the result can't be exactly represented as a floatingpoint number.
Examples:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main( void )
{
printf( "%f %f\n", fabs(.5), fabs(.5) );
return EXIT_SUCCESS;
}
produces the output:
0.500000 0.500000
Classification:
C11,
POSIX 1003.1
Safety: 

Cancellation point 
No 
Interrupt handler 
Yes 
Signal handler 
Yes 
Thread 
Yes 