---
name: "double_t"
section: "3type"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/double_t/3type"
---

# double\_t(3type)

most efficient floating types

## NAME

float\_t, double\_t - most efficient floating types

## LIBRARY

Math library (*libm*)

## SYNOPSIS

```
#include <math.h>
```

**typedef** /\* ... \*/ **float\_t;** **typedef** /\* ... \*/ **double\_t;**

## DESCRIPTION

The implementation's most efficient floating types at least as wide as *float* and *double* respectively. Their type depends on the value of the macro **FLT\_EVAL\_METHOD** (defined in *\<float.h\>*):

| | | |
| --- | --- | --- |
| **FLT\_EVAL\_METHOD** | *float\_t* | *double\_t* |
| 0 | *float* | *double* |
| 1 | *double* | *double* |
| 2 | *long double* | *long double* |

For other values of **FLT\_EVAL\_METHOD**, the types of *float\_t* and *double\_t* are implementation-defined.

## STANDARDS

C11, POSIX.1-2024.

## HISTORY

C99, POSIX.1-2001.

## SEE ALSO

**float.h**(0p), **math.h**(0p)