C++ primer plus学习笔记 (2) _simple File I/O

writing to text file

在头文件fstream中定义了一个ofstream的类(output file stream),这个类可以生成用于文件输出的对象.

不要搞混这里的输入和输出,output和input应该是针对于内存而言的,例如cout是从内存缓冲区到屏幕,ofstream是从内存缓冲区输出到文件.

可以参考标准输入来理解ofstream,如:
1.cout本身便是一个由ostream定义的对象(不是类),但是cout的定义隐藏在头文件中了.ofstream是一个类似于ostream的类,但是我们需要自己手动来定义一个对象.

2. ofstream这个element同样位于std命名空间内.

3. 使用ofstream类中的open方法来打开文件,从而绑定我们手动创建的对象和文件.

reading from file(input to memory)

#include <iostream>
#include <fstream>
//include some system funcs
#include <cstdlib>

const int SIZE = 60;// In C++,always using const variable to replace the #define
using namespace std;

int main(int argc, char *argv[])
{
    char filename[SIZE];
    ifstream inFile;
    cout << "please input the file name " << endl;
    cin.getline(filename,SIZE);//read a string not longer than the SIZE
    inFile.open(filename);//use the name array as the parameter
    //detecting the file is open or not
    if(!inFile.is_open())
    {
        cout << "the file is not open correctly !" <<endl;
        cout <<"TERMINATED" <<endl;
        exit(EXIT_FAILURE);//is Defined in cstdlib
    }
    double value;
    double sum = 0.0;
    int count = 0;
    inFile >> value;
    while(inFile.good())//inFile.good is familiar to isopen()
    {
        ++count;
        sum += value;
        inFile >> value;
    }

    if (inFile.eof())
    {
        cout << "sucussecfully read" << endl;
    }
        else if (inFile.fail())
            cout << "terminated by data mismatch" <<endl;
            else
                cout << "unknown erro" << endl;
    if(cout == 0)
    {
        cout << "no data" << endl;
    }
        else
            {
            cout << "items " << count << endl;
            cout << "sums " << sum <<endl;
            cout << "Average " << sum/count << endl;
    }

    //dont forget to close the file
    inFile.close();
    return 0;
}

以上代码来自原书，加上自己的一些注释。要注意的是是否正确打开的检查，以及用于检测异常的方法。