strtof(3)
NAME
strtod, strtof, strtold - convert ASCII string to floating-point number
SYNOPSIS
#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
DESCRIPTION
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).
RETURN VALUE
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.
ERRORS
ERANGE Overflow or underflow occurred.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────┼───────────────┼────────────────┤
│strtod(), strtof(), strtold() │ Thread safety │ MT-Safe locale │
└──────────────────────────────┴───────────────┴────────────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.
strtod() was also described in C89.
NOTES
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.
EXAMPLE
See the example on the strtol(3) manual page; the use of the functions
described in this manual page is similar.
SEE ALSO
atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3),
strtol(3), strtoul(3)
COLOPHON
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latest version of this page, can be found at
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