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);

   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,  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.

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.

EXAMPLE

       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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