C++文件流读写

流被用来读取/写入文件、连接网络和字符串，它的一个有用的特性是易于从混合数据类型中得到字符串。

#include<iostream>
#include<sstream>
#include<fstream>
int main() {
	using namespace std;
	ostringstream strbuf; //字符流声明
  
	int lucky = 7;
	float pi = 3.14;
	double e = 2.71;
	cout << "an in-memory stream" << endl;
  
	strbuf << "lucknumber" << lucky << endl//将各种类型的值和字符串一起传给字符流，然后再做统一处理
		<< "pi:" << pi << endl
		<< "e:" << e << endl;
  
	string strval = strbuf.str();//将字符串流转换成字符串
	cout << strval;//打印字符串
  
	ofstream outf;//声明openfile对象
	outf.open("mydata");//打开文件，没有则创建
	outf << strval;//将字符串流输出给文件
	outf.close();//关闭文件
  
  	cout << "read data from the file" << endl;//读文件
	string newstr;
	ifstream inf;//声明一个输入文件流对象
	inf.open("mydata");//打开文件
  
	if (inf) {//Make sure the filr exists before attempting to read
		while (! inf.eof()) {//文件流每次读取为一行，读取后会自动进入下一行，直到inf.eof()
			getline(inf, newstr);//把读取的每行当做字符串处理
			cout << newstr << endl;
		}
		inf.close();
	}
  
	cin.get();
	return 0;
}

QT中实现

#include<QTextStream>
#include<QString>
#include<QFile>

QTextStream cout(stdout);
QTextStream cerr(stderr);

int main()
{
    QString str,newstr;//Qstring为QT中的string，有丰富的API更好用
    QTextStream strbuf(&str);//QT的字符流声明
    int lucky =7;
    float pi =3.14;
    double e=2.71;

    cout<<"A in-memory stream"<<endl;
    strbuf<<"luckynumber:"<<lucky<<endl//一样先把字符都输入到字符流中，方便后面统一处理
         <<"pi:"<<pi<<endl
        <<"e:"<<e<<endl;
    cout<<str;

    QFile data("mydata");//创建QT文件类对象，并用文件初始化QFile对象
    data.open(QIODevice::WriteOnly);//打开文件，以QTIO的写方式
    QTextStream out(&data);//这里和VC不太一样，要输出到文件，先要将文件转换成对应的字符串流
    out<<str;//输出到已绑定字符流文件
    data.close();

    cout<<"Read from file line-by-line"<<endl;
    if(data.open(QIODevice::ReadOnly)){
        QTextStream in(&data);
        while (not in.atEnd()){
            newstr = in.readLine();
            cout<<newstr<<endl;
        }
        data.close();
    }


    return 0;
}

小试QT GUI

#include<QtGui>
#include<QMessageBox>
#include<QInputDialog>
#include <QApplication>
int main(int argc,char* argv[]){
    QApplication app(argc,argv);
    QTextStream cout(stdout);
    int answer = 0;
    do{
        int factArg=0;
        int fact(1);
      
        factArg = QInputDialog::getInt(0,"Factorial Calculator","Factorial of:",1);//QT的输入对话框
      
        cout<<"User entered:"<<factArg<<endl;//打印到控制台
      //业务内容
        int i =2;
        while(i<=factArg){
            fact=fact*i;
            ++i;
        }
      
        QString response=QString("The factorial of %1 is %2.\n%3")
                .arg(factArg).arg(fact)
                .arg("Do you want to computer another factorial?");//Qstring格式化字符串内容
      
        answer=QMessageBox::question(0,"play again?",response,
                QMessageBox::Yes|QMessageBox::No);//对话框设置

    }while(answer==QMessageBox::Yes);
    return EXIT_SUCCESS;
}

QString

可以将char类型的字符串用等号之间转换过来

#include<QTextStream>
#include<QString>

int main()
{
const char* charstr="this is a char string";
QTextStream cout(stdout);
QString str=charstr;
cout<<str<<endl;
return 0;
}