百度面试题：删除所有ascii编码的字符和数字

已知一个字串由GBK汉字和ascii编码的数字和字母混合组成，编写c语言函数实现从中去掉所有ascii编码的字母和数字(包括大小写)，要求在原字符串上返回结果。
例如： “http://hi.baidu.com/mianshiti 是讨论IT面试题的博客” 会变成 “://../ 是讨论面试题的博客”。
注：函数接口为：int filter_ascii(char* gbk)；汉字的GBK编码范围是0x8140-0xFEFE。

#include<iostream>
#include <cstdlib>

using namespace std;

int filter_ascii(char* gbk)
{
int new_p = 0;
int old_p = 0;

while(gbk[old_p])
{
if(gbk[old_p] > 0x81 || gbk[old_p] == 0x81 && gbk[old_p + 1] >= 0x40)
{
gbk[new_p++] = gbk[old_p++];
gbk[new_p++] = gbk[old_p++];
}
else if(gbk[old_p] >= 'a' && gbk[old_p] <= 'z' || gbk[old_p] >= 'A' && gbk[old_p] <= 'Z' || gbk[old_p] >= '0' && gbk[old_p] <= '9')
{
old_p++;
}
else
{
gbk[new_p++] = gbk[old_p++];
}
}
gbk[new_p] = '\0';
return 0;
}

int main()
{
char* gbk = "http://www.bupt.edu.cn/计算机学院";
filter_ascii(gbk);
cout << gbk << endl;
system("pause");
return 0;
}

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