## table of contents

STRTOD(3) | Linux Programmer's Manual | STRTOD(3) |

# NAME¶

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

# SYNOPSIS¶

**#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***);**

**strtof**(), **strtold**():

# DESCRIPTION¶

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).

# RETURN VALUE¶

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**, or **HUGE_VALL** is returned
(according to the return type and sign of the value), and **ERANGE** is
stored in *errno*.

If the correct value would cause underflow, a value with magnitude
no larger than **DBL_MIN**, **FLT_MIN**, or **LDBL_MIN** is
returned and **ERANGE** is stored in *errno*.

# ERRORS¶

**ERANGE**- Overflow or underflow occurred.

# ATTRIBUTES¶

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

Interface |
Attribute |
Value |

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

# CONFORMING TO¶

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

**strtod**() was also described in C89.

# NOTES¶

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.

# EXAMPLES¶

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

# SEE ALSO¶

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

# COLOPHON¶

This page is part of release 5.10 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/.

2020-11-01 | Linux |