strtof(3)

1STRTOD(3)                      Library functions                     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);
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13       #define _XOPEN_SOURCE 600   /* or #define _ISOC99_SOURCE */
14       #include <stdlib.h>
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16       float strtof(const char *nptr, char **endptr);
17       long double strtold(const char *nptr, char **endptr);
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DESCRIPTION

20       The  strtod(),  strtof(),  and  strtold() functions convert the initial
21       portion of the string pointed to by nptr to  double,  float,  and  long
22       double representation, respectively.
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24       The  expected  form  of the (initial portion of the) string is optional
25       leading white space as  recognized  by  isspace(3),  an  optional  plus
26       (``+'')  or minus sign (``-'') and then either (i) a decimal number, or
27       (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NAN  (not-a-
28       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 non-empty 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
38       nonempty  sequence  of  hexadecimal  digits possibly containing a radix
39       character, optionally followed by a binary exponent. A binary  exponent
40       consists  of  a  ``P''  or ``p'', followed by an optional plus or minus
41       sign, followed by a non-empty sequence of decimal digits, and indicates
42       multiplication  by  a  power of 2.  At least one of radix character and
43       binary exponent 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

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

68       ERANGE Overflow or underflow occurred.
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CONFORMING TO

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

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

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