程序6.16 sumafile.app

打开用户指定的文件，读取其中的数字，然后指出文件中包含多少个值以及它们的和与平均值。

#include<iostream>
#include<fstream>
#include<cstdlib>
const int SIZE = 60;
int main()
{
	using namespace std;
	char filename[SIZE];
	ifstream inFile;
	cout << "Enter name of data file: ";
	cin.getline(filename, SIZE);
	inFile.open(filename);
	if (!inFile.is_open())
	{
		cout << "Could not open the file " << filename << endl;
		cout << "Program terminating. \n";
		exit(EXIT_FAILURE);
	}
	double value;
	double sum = 0.0;
	int count = 0;

	inFile >> value;
	//while (inFile.good())
        while (inFile >> value)      //cin抽取字符返回值为cin
	{
		++count;
		sum += value;
	        //inFile >> value;
	}
	if (inFile.eof())
		cout << "End of file reached.\n";
	else if (inFile.fail())
		cout << "input terminated by data mismatch.\n";
	else
		cout << "Input terminated for unknown reason.\n";
	if (count == 0)
		cout << "No data processed.\n";
	else
	{
		cout << "Items read: " << count << endl;
		cout << "Sum: " << sum << endl;
		cout << "Average: " << sum / count << endl;
	}
	inFile.close();

	return 0;
}

知识点总结

1. inFile.is_open()：判断文件是否成功打开，若成功返回一个bool值；
2. exit()函数：在头文件cstdlib中定义，还定义了一个用于同操作系统通信的参数值EXIT_FAILURE，用于终止程序；
3. inFile.good()：文件是否读取成功，输出为布尔值；
4. inFile.eof()：文件是否到了文件尾；
5. inFile.fail()：文件与要求是否匹配。