strtod

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
       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, or HUGE_VALL is returned (according to the return type and
       sign of the value), and ERANGE is stored in errno.

       If the correct value would cause underflow, a value with magnitude no
       larger than DBL_MIN, FLT_MIN, or LDBL_MIN 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.

EXAMPLES
       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
       This page is part of release 5.09 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                              2020-11-01                          STRTOD(3)