Convert strings to double (atof), long double (_atold), integer (atoi), or long (atol).
| #include <math.h> | atof, _atold | |
| #include <stdlib.h> | atof, _atold, atoi, atol |
double atof( const char *string );
long double _atold( const char *string );
int atoi( const char *string);
long atol( const char *string);
| string | String to be converted |
These functions convert a character string to a double-precision floating-point value (atof), an integer value (atoi), a long integer value (atol), or a long double value (_atold). The input string is a sequence of characters that can be interpreted as a numerical value of the specified type.
The string size that can be handled by the atof or _atold function is limited to 100 characters.
The function stops reading the input string at the first character that it cannot recognize as part of a number. This character may be the null character ('\0') terminating the string.
The atof and _atold functions expect string to have the following form:
[[whitespace]] [[sign]] [[digits]] [[.digits]] [[{d |D | e | E}[[sign]]digits]]
A whitespace consists of space and/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 decimal point, at least one must appear after the decimal point. The decimal digits may be followed by an exponent, which consists of an introductory letter (d, D, e, or E) and an optionally signed decimal integer.
The atoi and atol functions do not recognize decimal points or exponents. The string argument for these functions has the form
[[whitespace]] [[sign]]digits
where whitespace, sign, and digits are exactly as described above for atof.
Each function returns the double, long double, int, or long value produced by interpreting the input characters as a number. The return value is 0 (for atoi), 0L (for atol), and 0.0 (for atof and _atold) if the input cannot be converted to a value of that type. The return value is undefined in case of overflow.
atof, atoi, atol
Standards:ANSI, UNIX
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
_atold
Standards:None
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
/* ATOF.C: This program shows how numbers stored as strings can be
* converted to numeric values using the atof, atoi, and atol functions.
*/
#include <stdlib.h>
#include <stdio.h>
void main( void )
{
char *s; double x; int i; long l;
s = " -2309.12E-15"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );
s = "7.8912654773d210"; /* Test of atof */
x = atof( s );
printf( "atof test: ASCII string: %s\tfloat: %e\n", s, x );
s = " -9885 pigs"; /* Test of atoi */
i = atoi( s );
printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );
s = "98854 dollars"; /* Test of atol */
l = atol( s );
printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
}
atof test: ASCII string: -2309.12E-15 float: -2.309120e-012
atof test: ASCII string: 7.8912654773d210 float: 7.891265e+210
atoi test: ASCII string: -9885 pigs integer: -9885
atol test: ASCII string: 98854 dollars long: 98854