STRTOD(3)



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);

   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 pos-
       sibly  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 char-
       acter used in the conversion is stored in the  location  referenced  by
       endptr.

       If  no  conversion is performed, zero is returned and 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 deter-
       mine 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 fol-
       lows "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 man-
       tissa 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), strtol(3), str-
       toul(3)

COLOPHON
       This page is part of release 4.05 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/.

Linux                             2016-03-15                         STRTOD(3)

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