STRTOD(3) BSD Library Functions Manual STRTOD(3)
strtod, strtof, strtold -- convert ASCII string to floating point
Standard C Library (libc, -lc)
strtod(const char *restrict nptr, char **restrict endptr);
strtof(const char *restrict nptr, char **restrict endptr);
strtold(const char *restrict nptr, char **restrict endptr);
These conversion functions convert the initial portion of the string pointed to by nptr to double, float, and long double representation,
The expected form of the string is an optional plus (``+'') or minus (``-'') sign, followed by either:
o a decimal significand, consisting of a sequence of decimal digits (optionally containing a decimal-point character) or
o a hexadecimal significand, consisting of a ``0X'' or ``0x'' followed by a sequence of hexadecimal digits (optionally containing a deci-
In both cases, the significand may be optionally followed by an exponent. An exponent consists of an ``E'' or ``e'' (for decimal constants)
or a ``P'' or ``p'' (for hexadecimal constants), followed by an optional plus or minus sign, followed by a sequence of decimal digits. For
decimal constants, the exponent indicates the power of 10 by which the significand should be scaled. For hexadecimal constants, the scaling
is instead done by powers of 2.
Alternatively, if the portion of the string following the optional plus or minus sign begins with ``INFINITY'' or ``NAN'', ignoring case, it
is interpreted as an infinity or a quiet NaN, respectively. The syntax ``NAN(s)'', where s is an alphanumeric string, produces the same
value as the call nan("s") (respectively, nanf("s") and nanl("s").)
In any of the above cases, leading white-space characters in the string (as defined by the isspace(3) function) are skipped. The decimal
point character is defined in the program's locale (category LC_NUMERIC).
Extended locale versions of these functions are documented in strtod_l(3). See xlocale(3) for more information.
The strtod(), strtof(), and strtold() 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
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, or HUGE_VALL is returned (according to the sign and type of the
return 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.
atof(3), atoi(3), atol(3), nan(3), strtod_l(3), strtol(3), strtoul(3), wcstod(3)
The strtod() function conforms to ISO/IEC 9899:1999 (``ISO C99'').
The author of this software is David M. Gay.
Copyright (c) 1998 by Lucent Technologies
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March 2, 2003 BSD