STRTOD(3) BSD Library Functions Manual STRTOD(3)NAME
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:
· a decimal significand consisting of a sequence of decimal digits
optionally containing a decimal-point character, or
· a hexadecimal significand consisting of a ``0X'' or ``0x'' followed
by a sequence of hexadecimal digits optionally containing a decimal-
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 signifi‐
cand 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).
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 charac‐
ter 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.
SEE ALSOatof(3), atoi(3), atol(3), nan(3), strtol(3), strtoul(3), wcstod(3)STANDARDS
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
All Rights Reserved
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