c 判断是否为 字母或数字（iswalnum example）

#include <stdio.h>
#include <wctype.h>
int main ()
{
    int i;
    wchar_t str[] = L"c3p。o...";
    i=0;
    while (iswalnum(str[i])){
        i++;
    }
    printf("The first %d characters are alphanumeric.
",i);
    return 0;
}

输出

The first 3 characters are alphanumeric.