c 判断一个字符是否为字母数字

#include <stdio.h>
#include <wctype.h>
int main ()
{
  int i;
  wchar_t str[] = L"c3po...";
  i=0;
  while (iswalnum(str[i])){ 
      i++;
  } 
  wprintf (L"The first %d characters are alphanumeric.
",i);
  return 0;
}

输出

The first 4 characters are alphanumeric.