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

```
#include <stdlib.h>
double strtod (char * nptr, char * *endptr);
float strtof (char * nptr, char * *endptr);
long double strtold (char * nptr, char * *endptr);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
strtof(),
strtold():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
```

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`

.

**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.

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

atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3), strtol(3), strtoul(3)

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/.