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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():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

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  mul‐
       tiplication by a power of 10.

       A  hexadecimal  number consists of a "0x" or "0X" followed by a nonempty sequence of hexa‐
       decimal 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  multiplica‐
       tion  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 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
   Multithreading (see pthreads(7))
       The strtod(), strtof(), and strtold() functions are thread-safe  with  exceptions.   These
       functions can be safely used in multithreaded applications, as long as setlocale(3) is not
       called to change the locale during their execution.

CONFORMING TO
       C89 describes strtod(), C99 describes the other two functions.

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  inter‐
       preted  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), strtol(3), strtoul(3)

COLOPHON
       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2014-08-19                                  STRTOD(3)


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