float_t, double_t

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Defined in header <math.h>
typedef /*implementation defined*/ float_t
 (since C99)
typedef /*implementation defined*/ double_t
 (since C99)

The types float_t and double_t are floating types at least as wide as float and double, respectively, and such that double_t is at least as wide as float_t. The value of FLT_EVAL_METHOD determines the types of float_t and double_t.

FLT_EVAL_METHOD Explanation
0 float_t and double_t are equivalent to float and double, respectively
1 both float_t and double_t are equivalent to double
2 both float_t and double_t are equivalent to long double
other both float_t and double_t are implementation defined

Example

Run this code
#include <float.h>
#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("%d\n", FLT_EVAL_METHOD);
    printf("%zu  %zu\n", sizeof(float),sizeof(float_t));
    printf("%zu  %zu\n", sizeof(double),sizeof(double_t));
    return 0;
}

Possible output: 

0
4  4
8  8

References

  • C11 standard (ISO/IEC 9899:2011):
  • 7.12 Mathematics <math.h> (p: 231)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12 Mathematics <math.h> (p: 212)