NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

STRTOD(3)                 Linux Programmer's Manual                STRTOD(3)

NAME         top

       strtod, strtof, strtold - convert ASCII string to floating-point num‐
       ber

SYNOPSIS         top

       #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         top

       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         top

       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         top

       ERANGE Overflow or underflow occurred.

ATTRIBUTES         top

       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         top

       POSIX.1-2001, POSIX.1-2008, C99.

       strtod() was also described in C89.

NOTES         top

       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         top

       See the example on the strtol(3) manual page; the use of the
       functions described in this manual page is similar.

SEE ALSO         top

       atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strtol(3),
       strtoul(3)

COLOPHON         top

       This page is part of release 4.07 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)