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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
STRTOD(3) Linux Programmer's Manual STRTOD(3)
strtod, strtof, strtold - convert ASCII string to floating-point num‐
ber
#include <stdlib.h>
double strtod(const char *nptr, char **endptr);
float strtof(const char *nptr, char **endptr);
long double strtold(const char *nptr, char **endptr);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strtof(), strtold():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
The strtod(), strtof(), and strtold() functions convert the initial
portion of the string pointed to by nptr to double, float, and long
double representation, respectively.
The expected form of the (initial portion of the) string is optional
leading white space as recognized by isspace(3), an optional plus
('+') or minus sign ('-') and then either (i) a decimal number, or
(ii) a hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-
a-number).
A decimal number consists of a nonempty sequence of decimal digits
possibly containing a radix character (decimal point, locale-
dependent, usually '.'), optionally followed by a decimal exponent.
A decimal exponent consists of an 'E' or 'e', followed by an optional
plus or minus sign, followed by a nonempty sequence of decimal
digits, and indicates multiplication by a power of 10.
A hexadecimal number consists of a "0x" or "0X" followed by a
nonempty sequence of hexadecimal digits possibly containing a radix
character, optionally followed by a binary exponent. A binary
exponent consists of a 'P' or 'p', followed by an optional plus or
minus sign, followed by a nonempty sequence of decimal digits, and
indicates multiplication by a power of 2. At least one of radix
character and binary exponent must be present.
An infinity is either "INF" or "INFINITY", disregarding case.
A NAN is "NAN" (disregarding case) optionally followed by a string,
(n-char-sequence), where n-char-sequence specifies in an
implementation-dependent way the type of NAN (see NOTES).
These functions return the converted value, if any.
If endptr is not NULL, a pointer to the character after the last
character used in the conversion is stored in the location referenced
by endptr.
If no conversion is performed, zero is returned and (unless endptr is
null) the value of nptr is stored in the location referenced by
endptr.
If the correct value would cause overflow, plus or minus HUGE_VAL
(HUGE_VALF, HUGE_VALL) is returned (according to the sign of the
value), and ERANGE is stored in errno. If the correct value would
cause underflow, zero is returned and ERANGE is stored in errno.
ERANGE Overflow or underflow occurred.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────┼───────────────┼────────────────┤
│strtod(), strtof(), strtold() │ Thread safety │ MT-Safe locale │
└──────────────────────────────┴───────────────┴────────────────┘
POSIX.1-2001, POSIX.1-2008, C99.
strtod() was also described in C89.
Since 0 can legitimately be returned on both success and failure, the
calling program should set errno to 0 before the call, and then
determine if an error occurred by checking whether errno has a
nonzero value after the call.
In the glibc implementation, the n-char-sequence that optionally
follows "NAN" is interpreted as an integer number (with an optional
'0' or '0x' prefix to select base 8 or 16) that is to be placed in
the mantissa component of the returned value.
See the example on the strtol(3) manual page; the use of the
functions described in this manual page is similar.
atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3),
strtol(3), strtoul(3)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-12-12 STRTOD(3)
Pages that refer to this page: gawk(1), pcpintro(1), pmstore(1), atof(3), atoi(3), nan(3), scanf(3), strfromd(3), strtol(3), strtoul(3), locale(7)