[cpp]: <fstream> - read_from_file

[cpp]:  <fstream> - read_from_file

 

 

 

 

一、介绍

 

　　1、介绍：从文件【big.cpp】读取内容，然后将【读取内容】输出到【屏幕】。

 

　　2、主程序源文件：iotest.cpp

 

　　3、被读取的文件：big.cpp

 

 

 

 

二、源代码

 

　　1、主程序源代码：iotest.cpp

/*    file_name = iotest.cpp
 *
 *    date = "2024-01-11"
 *
 * */


#include <iostream>
#include <fstream>
#include <string>
#include <locale>


using namespace std;


void read_from_keybord()
{
      string ptin = "[ Input a string ]: ";
      string ptout = "[ Output ]: ";
      string s ;
      cout << ptin << flush ;
      //cin >> s;
      getline(cin, s);
      cout << ptout << s << endl;
}


void read_from_file()
{
      // set buffer size
      char s[1020][1020];

      fstream to_stream;
      to_stream.open("big.cpp", ios::in);

      int end_file = 0;
      for(int i=0; to_stream.getline(s[i], 1000); i++){ end_file = i+1; }
      // set end of s[]
      s[end_file][0]='\n';

      for(int i=0; s[i][0]!='\n'; i++){ cout << i << "\t" << s[i] << endl; }

      to_stream.close();
}


int main(int argc, char *argv[], char *envp[])
{
      read_from_file();

      return 0;
}

 

　　2、被读取的文件：big.cpp

/*    file_name = big.cpp
 *
 *    date = "2024-01-11"
 *
 * */


#include <iostream>
#include <string>


using namespace std;


class name{};


class big :name
{
public:
      big() { cout << "big() "<< endl; }

      big(string n, string i, string f):name{n},id{i},info{f}
      { 
        cout << "    [constructor]: big(string, string, string) "<< endl; 
      }

      ~big(){ cout << "    [destructor]: ~big()" << endl;}

      void msg()
      { 
        cout <<"\tid := " << id << endl;  
        cout <<"\tname := " << name << endl;  
        cout <<"\tinfo := " << info << endl;  
      }

private:
      string name;
      string id;
      string info; 
};


int main(int argc, char *argv[], char *envp[])
{
      big b("file", "0xF0B1", "memory");
      b.msg();

      return 0;
}

 

 

三、运行结果

[wit@fedora io]$ alias | grep "gpp"
alias gpp='g++ -g -Wall -std=c++20 -o'
[wit@fedora io]$ 
[wit@fedora io]$ 
[wit@fedora io]$ gpp iotest iotest.cpp && ./iotest
0     /*        file_name = big.cpp
1      *
2      *        date = "2024-01-11"
3      *
4      * */
5
6
7     #include <iostream>
8     #include <string>
9
10
11    using namespace std;
12
13
14    class name{};
15
16
17    class big :name
18    {
19    public:
20      big() { cout << "big() "<< endl; }
21
22      big(string n, string i, string f):name{n},id{i},info{f}
23      { 
24              cout << "    [constructor]: big(string, string, string) "<< endl; 
25      }
26
27      ~big(){ cout << "    [destructor]: ~big()" << endl;}
28
29      void msg()
30      { 
31              cout <<"\tid := " << id << endl;  
32              cout <<"\tname := " << name << endl;  
33              cout <<"\tinfo := " << info << endl;  
34      }
35
36    private:
37      string name;
38      string id;
39      string info; 
40    };
41
42
43    int main(int argc, char *argv[], char *envp[])
44    {
45      big b("file", "0xF0B1", "memory");
46      b.msg();
47
48      return 0;
49    }
[wit@fedora io]$ 
[wit@fedora io]$ 
[wit@fedora io]$ gpp big big.cpp && ./big
    [constructor]: big(string, string, string) 
      id := 0xF0B1
      name := file
      info := memory
    [destructor]: ~big()
[wit@fedora io]$ 
[wit@fedora io]$ 
[wit@fedora io]$ 

 

 

四、参考资料

 

　　1、 getline()　　--　　https://cplusplus.com/reference/istream/istream/getline/