strtod, strtof, strtold - convert ASCII string to floating-point number

**#include <stdlib.h>**

**double strtod(const char ***`nptr`

**, char ****`endptr`

**);**

**float strtof(const char ***`nptr`

**, char ****`endptr`

**);**

**long double strtold(const char ***`nptr`

**, char ****`endptr`

**);**

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

The strtod(), strtof(), and strtold() functions convert the initial portion of the string pointed to by `nptr`

to `double`

, `float`

, and `long double`

representation, respectively.

The expected form of the (initial portion of the) string is optional leading white space as recognized by isspace(3), an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-a-number).

A `decimal number`

consists of a nonempty sequence of decimal digits possibly containing a radix character (decimal point, locale-dependent, usually '.'), optionally followed by a decimal exponent. A decimal exponent consists of an 'E' or 'e', followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 10.

A `hexadecimal number`

consists of a "0x" or "0X" followed by a nonempty sequence of hexadecimal digits possibly containing a radix character, optionally followed by a binary exponent. A binary exponent consists of a 'P' or 'p', followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 2. At least one of radix character and binary exponent must be present.

An `infinity`

is either "INF" or "INFINITY", disregarding case.

A `NAN`

is "NAN" (disregarding case) optionally followed by a string, `(n-char-sequence)`

, where `n-char-sequence`

specifies in an implementation-dependent way the type of NAN (see NOTES).

These functions return the converted value, if any.

If `endptr`

is not NULL, a pointer to the character after the last character used in the conversion is stored in the location referenced by `endptr`

.

If no conversion is performed, zero is returned and (unless `endptr`

is null) the value of `nptr`

is stored in the location referenced by `endptr`

.

If the correct value would cause overflow, plus or minus **HUGE_VAL** (**HUGE_VALF**, **HUGE_VALL**) is returned (according to the sign of the value), and **ERANGE** is stored in `errno`

. If the correct value would cause underflow, zero is returned and **ERANGE** is stored in `errno`

.

See the example on the strtol(3) manual page; the use of the functions described in this manual page is similar.

**ERANGE**Overflow or underflow occurred.

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |

strtod(), strtof(), strtold() | Thread safety | MT-Safe locale |

POSIX.1-2001, POSIX.1-2008, C99.

strtod() was also described in C89.

Since 0 can legitimately be returned on both success and failure, the calling program should set `errno`

to 0 before the call, and then determine if an error occurred by checking whether `errno`

has a nonzero value after the call.

In the glibc implementation, the `n-char-sequence`

that optionally follows "NAN" is interpreted as an integer number (with an optional '0' or '0x' prefix to select base 8 or 16) that is to be placed in the mantissa component of the returned value.

This page is part of release 4.15 of the Linux `man-pages`

project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.