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**NAME**

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

**SYNOPSIS**

#include<stdlib.h>doublestrtod(constchar*nptr,char**endptr);floatstrtof(constchar*nptr,char**endptr);longdoublestrtold(constchar*nptr,char**endptr);Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):strtof(),strtold(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

**DESCRIPTION**

Thestrtod(),strtof(), andstrtold() functions convert the initial portion of the string pointed to bynptrtodouble,float, andlongdoublerepresentation, respectively. The expected form of the (initial portion of the) string is optional leading white space as recognized byisspace(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). Adecimalnumberconsists 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. Ahexadecimalnumberconsists 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. Aninfinityis either "INF" or "INFINITY", disregarding case. ANANis "NAN" (disregarding case) optionally followed by a string,(n-char-sequence), wheren-char-sequencespecifies in an implementation-dependent way the type of NAN (see NOTES).

**RETURN** **VALUE**

These functions return the converted value, if any. Ifendptris not NULL, a pointer to the character after the last character used in the conversion is stored in the location referenced byendptr. If no conversion is performed, zero is returned and (unlessendptris null) the value ofnptris stored in the location referenced byendptr. If the correct value would cause overflow, plus or minusHUGE_VAL(HUGE_VALF,HUGE_VALL) is returned (according to the sign of the value), andERANGEis stored inerrno. If the correct value would cause underflow, zero is returned andERANGEis stored inerrno.

**ERRORS**

ERANGEOverflow or underflow occurred.

**ATTRIBUTES**

For an explanation of the terms used in this section, seeattributes(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 seterrnoto 0 before the call, and then determine if an error occurred by checking whethererrnohas a nonzero value after the call. In the glibc implementation, then-char-sequencethat 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.

**EXAMPLE**

See the example on thestrtol(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**

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