1STRTOD(3)                  Linux Programmer's Manual                 STRTOD(3)
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NAME

6       strtod, strtof, strtold - convert ASCII string to floating-point number
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SYNOPSIS

9       #include <stdlib.h>
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11       double strtod(const char *nptr, char **endptr);
12       float strtof(const char *nptr, char **endptr);
13       long double strtold(const char *nptr, char **endptr);
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15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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17       strtof(), strtold():
18           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
19           _POSIX_C_SOURCE >= 200112L;
20           or cc -std=c99
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DESCRIPTION

23       The strtod(), strtof(), and strtold() functions convert the initial
24       portion of the string pointed to by nptr to double, float, and long
25       double representation, respectively.
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27       The expected form of the (initial portion of the) string is optional
28       leading white space as recognized by isspace(3), an optional plus ('+')
29       or minus sign ('-') and then either (i) a decimal number, or (ii) a
30       hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-a-number).
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32       A decimal number consists of a nonempty sequence of decimal digits pos‐
33       sibly containing a radix character (decimal point, locale-dependent,
34       usually '.'), optionally followed by a decimal exponent.  A decimal
35       exponent consists of an 'E' or 'e', followed by an optional plus or
36       minus sign, followed by a nonempty sequence of decimal digits, and
37       indicates multiplication by a power of 10.
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39       A hexadecimal number consists of a "0x" or "0X" followed by a nonempty
40       sequence of hexadecimal digits possibly containing a radix character,
41       optionally followed by a binary exponent.  A binary exponent consists
42       of a 'P' or 'p', followed by an optional plus or minus sign, followed
43       by a nonempty sequence of decimal digits, and indicates multiplication
44       by a power of 2.  At least one of radix character and binary exponent
45       must be present.
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47       An infinity is either "INF" or "INFINITY", disregarding case.
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49       A NAN is "NAN" (disregarding case) optionally followed by '(', a
50       sequence of characters, followed by ')'.  The character string speci‐
51       fies in an implementation-dependent way the type of NAN.
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RETURN VALUE

54       These functions return the converted value, if any.
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56       If endptr is not NULL, a pointer to the character after the last char‐
57       acter used in the conversion is stored in the location referenced by
58       endptr.
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60       If no conversion is performed, zero is returned and the value of nptr
61       is stored in the location referenced by endptr.
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63       If the correct value would cause overflow, plus or minus HUGE_VAL
64       (HUGE_VALF, HUGE_VALL) is returned (according to the sign of the
65       value), and ERANGE is stored in errno.  If the correct value would
66       cause underflow, zero is returned and ERANGE is stored in errno.
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ERRORS

69       ERANGE Overflow or underflow occurred.
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CONFORMING TO

72       C89 describes strtod(), C99 describes the other two functions.
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NOTES

75       Since 0 can legitimately be returned on both success and failure, the
76       calling program should set errno to 0 before the call, and then deter‐
77       mine if an error occurred by checking whether errno has a nonzero value
78       after the call.
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EXAMPLE

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

85       atof(3), atoi(3), atol(3), strtol(3), strtoul(3)
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COLOPHON

88       This page is part of release 3.53 of the Linux man-pages project.  A
89       description of the project, and information about reporting bugs, can
90       be found at http://www.kernel.org/doc/man-pages/.
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94Linux                             2010-09-20                         STRTOD(3)
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