strtof(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 *restrict nptr, char **restrict endptr);
12       float strtof(const char *restrict nptr, char **restrict endptr);
13       long double strtold(const char *restrict nptr, char **restrict 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           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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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 ex‐
33       ponent consists of an 'E' or 'e', followed by an optional plus or minus
34       sign, followed by a nonempty sequence of decimal digits, and  indicates
35       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 string, (n-
48       char-sequence), where n-char-sequence specifies in  an  implementation-
49       dependent way the type of NAN (see NOTES).
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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 (unless endptr is
59       null) the value of nptr 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,  or  HUGE_VALL is returned (according to the return type and
63       sign of the value), and ERANGE is stored in errno.
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65       If the correct value would cause underflow, a value with  magnitude  no
66       larger  than  DBL_MIN,  FLT_MIN,  or LDBL_MIN is returned and ERANGE is
67       stored in errno.
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ERRORS

70       ERANGE Overflow or underflow occurred.
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ATTRIBUTES

73       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
74       tributes(7).
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76       ┌─────────────────────────────────────┬───────────────┬────────────────┐
77       │Interface                            │ Attribute     │ Value          │
78       ├─────────────────────────────────────┼───────────────┼────────────────┤
79       │strtod(), strtof(), strtold()        │ Thread safety │ MT-Safe locale │
80       └─────────────────────────────────────┴───────────────┴────────────────┘
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CONFORMING TO

83       POSIX.1-2001, POSIX.1-2008, C99.
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85       strtod() was also described in C89.
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NOTES

88       Since  0  can legitimately be returned on both success and failure, the
89       calling program should set errno to 0 before the call, and then  deter‐
90       mine if an error occurred by checking whether errno has a nonzero value
91       after the call.
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93       In the glibc implementation, the n-char-sequence that  optionally  fol‐
94       lows "NAN" is interpreted as an integer number (with an optional '0' or
95       '0x' prefix to select base 8 or 16) that is to be placed in the mantis‐
96       sa component of the returned value.
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EXAMPLES

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

107       This  page  is  part of release 5.12 of the Linux man-pages project.  A
108       description of the project, information about reporting bugs,  and  the
109       latest     version     of     this    page,    can    be    found    at
110       https://www.kernel.org/doc/man-pages/.
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114Linux                             2021-03-22                         STRTOD(3)