float_t, double_t - cppreference.com

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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

#include <float.h>
#include <math.h>
#include <stdio.h>

#define SHOW(expr) printf("%s = %d\n", #expr, (int)(expr))

int main()
{
    SHOW(FLT_EVAL_METHOD);
    SHOW(sizeof(float));
    SHOW(sizeof(float_t));
    SHOW(sizeof(double));
    SHOW(sizeof(double_t));
}

Possible output:

FLT_EVAL_METHOD = 1
sizeof(float) = 4
sizeof(float_t) = 8
sizeof(double) = 8
sizeof(double_t) = 8

References

C23 standard (ISO/IEC 9899:2024):

7.12 Mathematics <math.h> (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.12 Mathematics <math.h> (p: TBD)

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)

Example

References

See also