STRTOD(3) Linux Programmer's Manual STRTOD(3)
strtod, strtof, strtold - convert ASCII string to floating-point number
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)):
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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 pos-
sibly 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 char-
acter used in the conversion is stored in the location referenced by
If no conversion is performed, zero is returned and 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.
Multithreading (see pthreads(7))
The strtod(), strtof(), and strtold() functions are thread-safe with
exceptions. These functions can be safely used in multithreaded appli-
cations, as long as setlocale(3) is not called to change the locale
during their execution.
C89 describes strtod(), C99 describes the other two functions.
Since 0 can legitimately be returned on both success and failure, the
calling program should set errno to 0 before the call, and then deter-
mine 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 fol-
lows "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 man-
tissa 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), strtol(3), str-
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Linux 2014-08-19 STRTOD(3)