Return Value
strtod returns the value of the floating-point number, except when the representation would cause an overflow, in which case the function returns +/–HUGE_VAL. The sign of HUGE_VAL matches the sign of the value that cannot be represented. strtod returns 0 if no conversion can be performed or an underflow occurs.
strtol returns the value represented in the string nptr, except when the representation would cause an overflow, in which case it returns LONG_MAX or LONG_MIN. strtoul returns the converted value, if any, or ULONG_MAX on overflow. Each of these functions returns 0 if no conversion can be performed.
wcstod, wcstol, and wcstoul return values analogously to strtod, strtol, and strtoul, respectively.
For all six functions in this group, errno is set to ERANGE if overflow or underflow occurs.
Parameters
nptr
Null-terminated string to convert
endptr
Pointer to character that stops scan
base
Number base to use
Remarks
The strtod, strtol, and strtoul functions convert nptr to a double-precision value, a long-integer value, or an unsigned long-integer value, respectively.
The input string nptr is a sequence of characters that can be interpreted as a numerical value of the specified type. Each function stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character. For strtol or strtoul, this terminating character can also be the first numeric character greater than or equal to base.
For all six functions in the strtod group, the current locale’s LC_NUMERIC category setting determines recognition of the radix character in nptr; for more information, see setlocale. If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location pointed to by endptr.
strtod expects nptr to point to a string of the following form:
[whitespace] [sign] [digits] [.digits] [ {d | D | e | E}[sign]digits]
A whitespace may consist of space or tab characters, which are ignored; sign is either plus (+) or minus (–); and digits are one or more decimal digits. If no digits appear before the radix character, at least one must appear after the radix character. The decimal digits can be followed by an exponent, which consists of an introductory letter (d, D, e, or E) and an optionally signed integer. If neither an exponent part nor a radix character appears, a radix character is assumed to follow the last digit in the string. The first character that does not fit this form stops the scan.
The strtol and strtoul functions expect nptr to point to a string of the following form:
[whitespace] [{+ | –}] [0 [{ x | X }]] [digits]
If base is between 2 and 36, then it is used as the base of the number. If base is 0, the initial characters of the string pointed to by nptr are used to determine the base. If the first character is 0 and the second character is not 'x' or 'X', the string is interpreted as an octal integer; otherwise, it is interpreted as a decimal number. If the first character is '0' and the second character is 'x' or 'X', the string is interpreted as a hexadecimal integer. If the first character is '1' through '9', the string is interpreted as a decimal integer. The letters 'a' through 'z' (or 'A' through 'Z') are assigned the values 10 through 35; only letters whose assigned values are less than base are permitted. strtoul allows a plus (+) or minus (–) sign prefix; a leading minus sign indicates that the return value is negated.
wcstod, wcstol, and wcstoul are wide-character versions of strtod, strtol, and strtoul, respectively; the nptr argument to each of these wide-character functions is a wide-character string. Otherwise, each of these wide-character functions behaves identically to its single-byte–character counterpart.
Example
/* STRTOD.C: This program uses strtod to convert a
* string to a double-precision value; strtol to
* convert a string to long integer values; and strtoul
* to convert a string to unsigned long-integer values.
*/
#include <stdlib.h>
#include <stdio.h>
void main( void )
{
char *string, *stopstring;
double x;
long l;
int base;
unsigned long ul;
string = "3.1415926This stopped it";
x = strtod( string, &stopstring );
printf( "string = %s\n", string );
printf(" strtod = %f\n", x );
printf(" Stopped scan at: %s\n\n", stopstring );
string = "-10110134932This stopped it";
l = strtol( string, &stopstring, 10 );
printf( "string = %s", string );
printf(" strtol = %ld", l );
printf(" Stopped scan at: %s", stopstring );
string = "10110134932";
printf( "string = %s\n", string );
/* Convert string using base 2, 4, and 8: */
for( base = 2; base <= 8; base *= 2 )
{
/* Convert the string: */
ul = strtoul( string, &stopstring, base );
printf( " strtol = %ld (base %d)\n", ul, base );
printf( " Stopped scan at: %s\n", stopstring );
}
}
Output
string = 3.1415926This stopped it
strtod = 3.141593
Stopped scan at: This stopped it
string = -10110134932This stopped it strtol = -2147483647 Stopped scan at: This stopped itstring = 10110134932
strtol = 45 (base 2)
Stopped scan at: 34932
strtol = 4423 (base 4)
Stopped scan at: 4932
strtol = 2134108 (base 8)
Stopped scan at: 932
Data Conversion Routines | Floating-Point Support Routines | Locale Routines
See Also atof, localeconv, setlocale