20240507_ClassDemo_23-4.rar

/* Ch13: 文件输入输出 cin: console input, 控制台输入/标准输入/键盘输入 cout: console output, 控制台输出/标准输出/屏幕输出 */ #include <iostream> //input output stream, for cin, cout, ... #include <fstream> //file stream, for ifstream, ofstream #include <string> //for string class using namespace std; int main() { //open the file char fileName[200] = "a.txt"; ifstream fin; fin.open(fileName); if(fin.fail()) //if(!fin) { cout << "Failed to open the file: " << fileName << endl; return 0; } //read/write the file /*逐字符读取 char c; //while(fin >> c)//不包含分隔符(空格/制表符/换行符) while(fin.get(c))//包含分隔符(空格/制表符/换行符) { cout << c; } */ /*逐段/单词读取 //char str[200] = ""; string str = ""; while(fin >> str) { cout << str << endl; } */ /*逐行读取 char str[200] = ""; while(fin.getline(str, 200)) { cout << str << endl; } */ string str = ""; while(getline(fin, str)) { cout << str << endl; } //close the file fin.close(); return 0; } int main3() { //open the file char fileName[200] = "a.txt"; //ifstream fin; //fin.open(fileName); //fin.open(fileName, ios::in); ifstream fin(fileName); //ifstream fin(fileName, ios::in); //read/write the file //int a, b; //fin >> a >> b; //cout << "a = " << a << " , b = " << b << endl; int a, sum = 0; while( fin >> a ) { sum += a; //cout << a << endl; } cout << "sum = " << sum << endl; //close the file fin.close(); return 0; } int main2() { /* cout << "e:\demo\a.txt" << endl; cout << "e:\\demo\\a.txt" << endl; cout << "e:/demo\\a.txt" << endl; cout << "e:\\demo/a.txt" << endl; cout << "e:/demo/a.txt" << endl; return 0; */ //open the file char fileName[200] = "a.txt";//相对路径 //char fileName[200] = "E:\\demo\\a.txt";//绝对路径 //char fileName[200] = "E:/demo\\a.txt";//绝对路径 //char fileName[200] = "E:\\demo/a.txt";//绝对路径 //char fileName[200] = "E:/demo/a.txt";//绝对路径 //char fileName[200] = "E:/demo/test/a.txt";//绝对路径 ofstream fout; //fout.open(fileName); fout.open(fileName, ios::app); //if(fout.fail()) if(!fout) { cout << "Failed to open the file: " << fileName << endl; return 0; } //ofstream fout; //fout.open("a.txt");//默认是截断/覆盖写入模式 //fout.open("a.txt", ios::out);//output,截断/覆盖写入模式 //fout.open("a.txt", ios::trunc);//truncate,截断/覆盖写入模式 //fout.open("a.txt", ios::app);//append,追加/附加写入模式 //ofstream fout("a.txt"); //ofstream fout("a.txt", ios::app); //read/write the file fout << "Hello world!" << endl; //close the file fout.close(); return 0; } int main1() { int a; cin >> a; cout << "a = " << a << endl; return 0; }