strtod(3)

1strtod(3)                  Library Functions Manual                  strtod(3)
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NAME

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

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <stdlib.h>
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14       double strtod(const char *restrict nptr, char **restrict endptr);
15       float strtof(const char *restrict nptr, char **restrict endptr);
16       long double strtold(const char *restrict nptr, char **restrict endptr);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       strtof(), strtold():
21           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

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

55       These functions return the converted value, if any.
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57       If  endptr is not NULL, a pointer to the character after the last char‐
58       acter used in the conversion is stored in the  location  referenced  by
59       endptr.
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61       If  no  conversion is performed, zero is returned and (unless endptr is
62       null) the value of nptr is stored in the location referenced by endptr.
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64       If the correct value would cause  overflow,  plus  or  minus  HUGE_VAL,
65       HUGE_VALF,  or  HUGE_VALL is returned (according to the return type and
66       sign of the value), and ERANGE is stored in errno.
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68       If the correct value would cause underflow, a value with  magnitude  no
69       larger  than  DBL_MIN,  FLT_MIN,  or LDBL_MIN is returned and ERANGE is
70       stored in errno.
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ERRORS

73       ERANGE Overflow or underflow occurred.
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ATTRIBUTES

76       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
77       tributes(7).
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79       ┌─────────────────────────────────────┬───────────────┬────────────────┐
80       │Interface                            │ Attribute     │ Value          │
81       ├─────────────────────────────────────┼───────────────┼────────────────┤
82       │strtod(), strtof(), strtold()        │ Thread safety │ MT-Safe locale │
83       └─────────────────────────────────────┴───────────────┴────────────────┘
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VERSIONS

86       In  the  glibc implementation, the n-char-sequence that optionally fol‐
87       lows "NAN" is interpreted as an integer number (with an optional '0' or
88       '0x' prefix to select base 8 or 16) that is to be placed in the mantis‐
89       sa component of the returned value.
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STANDARDS

92       C11, POSIX.1-2008.
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HISTORY

95       strtod()
96              C89, POSIX.1-2001.
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98       strtof()
99       strtold()
100              C99, POSIX.1-2001.
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NOTES

103       Since 0 can legitimately be returned on both success and  failure,  the
104       calling  program should set errno to 0 before the call, and then deter‐
105       mine if an error occurred by checking whether errno has a nonzero value
106       after the call.
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EXAMPLES

109       See  the example on the strtol(3) manual page; the use of the functions
110       described in this manual page is similar.
111