In C, fabs() returns the absolute value of a double. It drops a minus sign and keeps the size. fabs(-3.5) is 3.5.
You pass one double. The result is a double that is never negative. Include <math.h>. For an int, use abs().
Pass the floating-point number. Start with this call.
fabs(-3.5);| Call | What it does |
|---|---|
fabs(-3.5) | Drops the minus sign and returns 3.5. |
Include <math.h>. On GCC, link with -lm. Do not use abs() for a double.
double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);| Parameter | Description |
|---|---|
| x | Required. The double whose sign you want to drop. |
| Return Value | Description |
|---|---|
| Non-negative double | The same magnitude, with the minus sign removed. |
Flip negatives; leave positives unchanged.
#include <stdio.h>
#include <math.h>
int main(void) {
printf("%.2f\n", fabs(-12.34));
printf("%.2f\n", fabs(3.5));
return 0;
}fabs.-12.34 becomes 12.34.3.5 stays 3.5.double.Absolute difference gives a distance that does not depend on order.
#include <stdio.h>
#include <math.h>
int main(void) {
double a = 3.0;
double b = 10.0;
double d = fabs(a - b);
printf("distance = %.1f\n", d);
return 0;
}a - b is -7.0.7.0.fabs(b - a) is the same distance.Floating-point values rarely match exactly. Compare with a small allowed error.
#include <stdio.h>
#include <math.h>
int main(void) {
double x = 0.1 + 0.2;
double eps = 1e-9;
if (fabs(x - 0.3) < eps) {
printf("close enough\n");
} else {
printf("not close\n");
}
return 0;
}0.3 exactly.fabs(x - 0.3) is a tiny error.1e-9, treat them as equal.Round a floating-point value toward negative infinity.
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