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

# strfromd(3)

string from float

## NAME

strfromd, strfromf, strfroml - string from float

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdlib.h>
```

**int strfromd(**size\_t n;              **char** *str***\[restrict** *n***\], size\_t** *n***,**              **const char \*restrict** *format***, double** *fp***);** **int strfromf(**size\_t n;              **char** *str***\[restrict** *n***\], size\_t** *n***,**              **const char \*restrict** *format***, float** *fp***);** **int strfroml(**size\_t n;              **char** *str***\[restrict** *n***\], size\_t** *n***,**              **const char \*restrict** *format***, long double** *fp***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**strfromd**(), **strfromf**(), **strfroml**():

```
    __STDC_WANT_IEC_60559_BFP_EXT__
```

## DESCRIPTION

These functions convert a floating-point value, *fp*, into a string of characters, *str*, with a configurable *format* string. At most *n* characters are stored into *str*.

The terminating null byte ('\\0') is written if and only if *n* is sufficiently large, otherwise the written string is truncated at *n* characters.

The **strfromd**(), **strfromf**(), and **strfroml**() functions are equivalent to

```
snprintf(str, n, format, fp);
```

except for the *format* string.

### Format of the format string

The *format* string must start with the character '%'. This is followed by an optional precision which starts with the period character (.), followed by an optional decimal integer. If no integer is specified after the period character, a precision of zero is used. Finally, the format string should have one of the conversion specifiers **a**, **A**, **e**, **E**, **f**, **F**, **g**, or **G**.

The conversion specifier is applied based on the floating-point type indicated by the function suffix. Therefore, unlike **snprintf**(), the format string does not have a length modifier character. See [**snprintf**(3)](/snprintf/3.md) for a detailed description of these conversion specifiers.

The implementation conforms to the C99 standard on conversion of NaN and infinity values:

If *fp* is a NaN, +NaN, or -NaN, and **f** (or **a**, **e**, **g**) is the conversion specifier, the conversion is to "nan", "nan", or "-nan", respectively. If **F** (or **A**, **E**, **G**) is the conversion specifier, the conversion is to "NAN" or "-NAN".

Likewise if *fp* is infinity, it is converted to \[-\]inf or \[-\]INF.

A malformed *format* string results in undefined behavior.

## RETURN VALUE

The **strfromd**(), **strfromf**(), and **strfroml**() functions return the number of characters that would have been written in *str* if *n* had enough space, not counting the terminating null byte. Thus, a return value of *n* or greater means that the output was truncated.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md) and the **POSIX Safety Concepts** section in GNU C Library manual.

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **strfromd**(), **strfromf**(), **strfroml**() | Thread safety | MT-Safe locale |
|  | Async-signal safety | AS-Unsafe heap |
|  | Async-cancel safety | AC-Unsafe mem |

Note: these attributes are preliminary.

## STANDARDS

ISO/IEC TS 18661-1.

## VERSIONS

- **strfromd**() **strfromf**() **strfroml**()

  glibc 2.25.

## NOTES

These functions take account of the **LC\_NUMERIC** category of the current locale.

## EXAMPLES

To convert the value 12.1 as a float type to a string using decimal notation, resulting in "12.100000":

```
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <stdlib.h>
int ssize = 10;
char s[ssize];
strfromf(s, ssize, "%f", 12.1);
```

To convert the value 12.3456 as a float type to a string using decimal notation with two digits of precision, resulting in "12.35":

```
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <stdlib.h>
int ssize = 10;
char s[ssize];
strfromf(s, ssize, "%.2f", 12.3456);
```

To convert the value 12.345e19 as a double type to a string using scientific notation with zero digits of precision, resulting in "1E+20":

```
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <stdlib.h>
int ssize = 10;
char s[ssize];
strfromd(s, ssize, "%.E", 12.345e19);
```

## SEE ALSO

[**atof**(3)](/atof/3.md), [**snprintf**(3)](/snprintf/3.md), [**strtod**(3)](/strtod/3.md)