c++之输出文件和输入文件的处理

1 例如：
2         ofstream  ofile ;        // 创建输出文件流
3         ofile . open ( "myfile1" ) ;    // ofile流与文件“myfile1”相关联，等价于Ofstream ofile（“myfile1”）；
4         ……            // 访问文件“myfile1”
5         ofile . close ( ) ;// close函数关闭文件“myfile1”，但流对象任然存在          
6         ofile . open ( "myfile2" );     // 重用ofile流
7             

 1 #include <iostream>
 2 #include <fstream>
 3 using namespace std;
 4 
 5 void main()
 6 {
 7     ofstream ost;    //创建输出流对象
 8     ost.open("d:\\xiaoxue");//建立文件关联，缺省为文件模式
 9     ost << 20 << endl;    //向流插入数据
10     ost << 3.5 << endl;
11     ost.close();    //关闭文件
12     ifstream ist("d:\\xiaoxue");    ;//创建输入流并建立文件关联，
13     int n;
14     double d;
15     ist >> n >> d;    //从流提取数据
16     cout << n  <<  ‘\t‘ << d << endl;    //向预定义流插入数据
17 }

 1 #include <iostream>
 2 #include <fstream>
 3 #include <iomanip>
 4 using namespace std;
 5 
 6 void main()
 7 {
 8     ofstream ost("d:\\my.txt");//默认方式打开文本文件
 9     ost << "1234567890" << endl;    //插入字符串
10     int a = 123;//把整形数转换成字符串
11     ost << a << endl;
12     
13     //以指定格式插入数据
14     ost << setw(10) << a << endl;
15     //关闭右对齐，设置左对齐，设置填充符号，设置域宽，
16     ost << resetiosflags(ios::right) << setiosflags(ios::left) << setfill(‘*‘) << setw(10) << a << endl;
17     //关闭左对齐，设置右对齐，设置精度，设置域宽
18     ost << resetiosflags(ios::left) << setiosflags(ios::right) << setprecision(6) << setw(10) << 12.34567890 << endl;
19     //关闭文件
20     ost.close();
21 }

 1 #include <fstream>
 2 #include <iostream>
 3 using namespace std;
 4 //复制文件
 5 int main()
 6 {
 7     ifstream ist("d:\\test.txt");
 8     if(!ist)
 9     {
10         cout << "Connot open ‘text‘ of input"<<endl;
11         return 0;
12     }
13     ofstream ost("d:\\test1.txt");
14     if(!ost)
15     {
16         cout << "Connot open file!" << endl;
17         return 0;
18     }
19     char ch;
20     while(ist && ist.get(ch))
21     {
22         ost.put(ch);
23     }
24     ost.close();
25     ist.close();
26     return 1;
27 }

1 #include <fstream>
2 using namespace std;
3 void main()
4 {
5     ofstream ost("d:\\test1.txt",ios::app);//追加方式
6     char s[20] ="\tStraightforward!";
7     ost << s;    //插入字符串
8     ost.close();
9 }

 1 #include <iostream>
 2 #include <fstream>
 3 using namespace std;
 4 
 5 void main()
 6 {
 7     char fileName[30],name[30],num[30],title[50];
 8     int n=0;
 9     double max,min,ave,total=0,score;
10     cout << "Please input the name of students file!"<< endl;
11     cin >> fileName;
12     ofstream ost(fileName,ios::out);
13     if(!ost)
14     {
15         cout<< "File could not be open!"<<endl;
16     }
17     ifstream ist(fileName,ios::in);
18     if(!ist)
19     {
20         cout << "File could not be open!" << endl;
21     }
22     ost << "\t\t\t\t\t\t学生成绩文件\n";
23     cout << "Input num、name and score:(Enter Ctrl-Z to end input.)\n";
24     while(cin >> num >> name >> score)
25     {
26         ost << num <<‘\t‘ << name << ‘\t‘ << score << ‘\n‘;
27     }
28     ost.close();
29     ist.getline(title,40);//略去标题行
30     while(ist >> num >> name >> score)    //提取数据
31     {
32         cout << num << ‘\t‘ << name << ‘\t‘ << score << endl;
33         if(n==0)
34         {
35             min = max = score;
36         }else
37         {
38             if(score>max)
39             {
40                 max = score;
41             }
42             if(score<min)
43             {
44                 min = score;
45             }
46         }
47         n++;
48         total +=score;    //统计
49     }
50     ave = total/n;
51     cout<< "maximal is" << max << "\n" << "minimal is" << min << ‘\n‘ << "average is" << ave << endl;
52     ist.close();
53 }

 1 #include <iostream>
 2 #include <fstream>
 3 using namespace std;
 4 void main()
 5 {
 6     void browseFile(char*,int);
 7     char fileName[40];
 8     cout << "Please input name of file！"<<endl;
 9     cin>>fileName;
10     browseFile(fileName,1);
11 }
12 void browseFile(char *fileName,int delLine)
13 {
14     ifstream ist(fileName,ios::in);
15     char s[80];
16     for(int i=1;i<=delLine;i++)
17     {
18         ist.getline(s,80);
19     }    //不显示开始指定的行数
20     while(!ist.eof())
21     {
22         ist.getline(s,80);//按行读取文件
23         cout << s << endl;//按行显示文件
24     }
25     ist.close();
26 }