NAME

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

SYNOPSIS

       #include <stdlib.h>

       double strtod(const char *restrict nptr, char **restrict endptr);
       float strtof(const char *restrict nptr, char **restrict endptr);
       long double strtold(const char *restrict nptr, char **restrict endptr);

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

       strtof(), strtold():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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

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       found at https://www.kernel.org/doc/man-pages/.