c++ 输入流

open file

ifstream in;

in.open("input.txt");　　//parameter is uchar*! just correspond with the main parameter, argv[1].

ifstream& openFile(ifstream& inf, const char* pN)
{
    inf.close();        //close flow
    inf.clear();        //clear any existing error
    //combine inf and file, open file.
    inf.open( pN );

    return inf;    
}
ifstream& openFile(ifstream& inf, const string& pN)
{
    inf.close();        //close flow
    inf.clear();        //clear any existing error
    //combine inf and file, open file.
    inf.open( pN.c_str());    //!!must convers string into uchar*

    return inf;    
}    

如果文件打开成功，则上述函数返回值（inf)有效。 同cin

if(!openFile( ......) )

//文件打开没有成功， 终止允许。

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2 cin

 cin.clear();   //使得输入流有效   
 cin.sync();   //清空输入流缓冲中无效的数据   // it is a must