strtod(3)

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():   _XOPEN_SOURCE >= 600   ||  _ISOC99_SOURCE;  or
18       cc -std=c99
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DESCRIPTION

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

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

67       ERANGE Overflow or underflow occurred.
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CONFORMING TO

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

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

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

86       This page is part of release 3.25 of the Linux  man-pages  project.   A
87       description  of  the project, and information about reporting bugs, can
88       be found at http://www.kernel.org/doc/man-pages/.
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92Linux                             2007-07-26                         STRTOD(3)