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expm1, expm1f, expm1l

Computes the base-e exponential of a value, minus one.


double expm1(
   double x
float expm1(
   float x
);  // C++ only
long double expm1(
   long double x
);  // C++ only
float expm1f(
   float x
long double expm1l(
   long double x
#define expm1(X) // Requires C11 or higher


The floating-point exponential value.

Return value

The expm1 functions return a floating-point value that represents ex - 1, if successful. On overflow, expm1 returns HUGE_VAL, expm1f returns HUGE_VALF, expm1l returns HUGE_VALL, and errno is set to ERANGE. For more information about return codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.


Because C++ allows overloading, you can call overloads of expm1 that take and return float and long double values. In a C program, unless you're using the <tgmath.h> macro to call this function, expm1 always takes and returns a double.

If you use the <tgmath.h> expm1() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.


Routine Required header
expm1, expm1f, expm1l <math.h>
expm1 macro <tgmath.h>

For more compatibility information, see Compatibility.

See also

Math and floating-point support
exp2, exp2f, exp2l
pow, powf, powl