友元重载问题

我在类chaoshu中声明friend long operator =(long&,chaoshu &);
却出现错误： 'operator =(long&,chaoshu &)'must be a member function
请问怎么回事？那位大神帮帮忙啊！
以下为原文:
class chaoshu
{
private:
char sp;
char vol[128];
int len;
public:
chaoshu(){sp=len=0;}
chaoshu(long);
char operator ==(chaoshu &);
char operator >(chaoshu &);
char operator <(chaoshu &);
chaoshu operator -(chaoshu &);
chaoshu operator +(chaoshu &);
chaoshu operator *(chaoshu &);
chaoshu operator /(long);
long operator %(long);
chaoshu operator /(chaoshu &);
friend long operator =(long&,chaoshu &);
friend char* operator =(char*,chaoshu &);
void show();
};
long operator =(long &s,chaoshu &u)
{
long d=0;
int i;
for(i=u.len-1;i>=0;i--)d=d*10+u.vol[i];
s=d;
return d;
}
char* operat

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