if(!infile){ //判断文件是否打开
cerr<<"error:unable to open input file!\n";
exit(-1);
}
if(!outfile){
cerr<<"eroor:unble to open output file!\n";
exit(-2);
}
if(!outfile2){
cerr<<"error:unable to open input file!\n";
exit(-3);
}
//初始化 a 用于建立huffman_tree
const int num=94;
statrstics a[num];
for(int i=0,j=32;i<=94;++i,++j)
{
a[i].letter=j;
a[i].weight=0;
}