先用String里的c_ptr把string对象变为const char*,然后用下面的一些函数可以转换。
/* 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 );
}
Output