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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 (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).

     allbox;  lbw29  lb  lb  l  l l.  Interface Attribute Value T{ strtod(),
     strtof(), strtold() T}   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.