#include<iostream>
#include<string>
#include"playpen.h"
using namespace std;

int getint( istream&source ){
  int temp;
  source>>temp;
  if(source.fail() ){
     source.clear();
     cerr<<"corrupted data stream accessed in getint.\n";
     throw fgw::problem("corrupted data stream.");
    }
    else return temp;
}
这个程序运行时为什么出现如下错误啊？
mingw/bin/../lib/gcc-lib/mingw32/3.2.3/../../../libmingw32.a(main.o)(.text+0x97):main c:undefined reference to'WinMain@16'