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
7

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           _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).
29
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 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,  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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ATTRIBUTES

70       For   an   explanation   of   the  terms  used  in  this  section,  see
71       attributes(7).
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73       ┌──────────────────────────────┬───────────────┬────────────────┐
74       │Interface                     │ Attribute     │ Value          │
75       ├──────────────────────────────┼───────────────┼────────────────┤
76       │strtod(), strtof(), strtold() │ Thread safety │ MT-Safe locale │
77       └──────────────────────────────┴───────────────┴────────────────┘

CONFORMING TO

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

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

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

103       This page is part of release 5.02 of the Linux  man-pages  project.   A
104       description  of  the project, information about reporting bugs, and the
105       latest    version    of    this    page,    can     be     found     at
106       https://www.kernel.org/doc/man-pages/.
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110Linux                             2017-09-15                         STRTOD(3)