freopen () Redirection

freopen function:

        Using a different file or reopen the flow pattern, i.e. redirection

 

C++

 

   //把一个字符串写入到文件中去：
#include<iostream>
using namespace std;

int main(void)
{
    /* redirect standard output to a file */
    if(freopen("D:\\out.txt", "w", stdout) == NULL)
        fprintf(stderr,"error redirecting stdout\n");
    /* this output will go to a file */
    printf("This will go into a file.\n");
    string s = "12345";
    cout<<s<<endl; 
    int a,b;
    while(cin>>a>>b){
        cout<<a<<b<<endl; 
    }
    /*close the standard output stream*/
    fclose(stdout);
    return 0;
}

View Code

 

#include <the iostream>
 the using  namespace STD; 

int main ( void ) 
{ 
    the FILE * FP; 
    FP = The freopen ( " D: \\ in.txt " , " R & lt " , stdin);    // The freopen () return value, if establish a connection to the file fails, return NULL 
    
    IF (FP = NULL!) {             // file connection is established 
        int C; 
        CIN >> C;              // read data from a file 
        COUT C << << endl;       // in the display data on the screen 
    } the else { 
        COUT << "Open Error"<<endl;
    }
    
    //输出到控制台“CON”
    fp = freopen("CON","r",stdin);
    int a, b;
    cin>>a>>b;
    cout<<a<<b<<endl<<endl;  
    return 0;
}

View Code

#include<iostream>
using namespace std;

int main()
{
    
    freopen("D:\\in.txt", "r", stdin);
    freopen("D:\\out.txt", "w", stdout);
    
    int a, b;
    while (cin >> a >> b)
        cout << a + b << endl;
    fclose(stdin);
    
    fclose(stdout);

    return 0;
}

View Code

#include<iostream>
using namespace std;

int main()
{
    int a, b;
    freopen("D:\\in.txt", "r", stdin);
    freopen("D:\\out.txt", "w", stdout);
    while (scanf("%d%d", &a, &b) == 2)
        printf("%d\n", a + b);
    fclose(stdin);
    fclose(stdout);

    return 0;
}

View Code

#include<iostream>
using namespace std;

int main()
{
    int a, b;
    freopen("D:\\in.txt", "r", stdin);
    freopen("D:\\out.txt", "w", stdout);
    while (scanf("%d%d", &a, &b) == 2)
        printf("%d\n", a + b);
    //fclose(stdin);
    //fclose(stdout);
    freopen("CON", "r", stdin);
    freopen("CON", "w", stdout);
    printf("Hello World\n");
    scanf("%d%d", &a,&b);

    return 0;
}

View Code

#include<iostream>
using namespace std;

int main()
{
    int a, b;
    freopen("D:\\in.txt", "r", stdin);
    freopen("D:\\out.txt", "w", stdout);
    while (scanf("%d%d", &a, &b) == 2)
        printf("%d\n", a + b);
    //fclose(stdin);
    //fclose(stdout);
    freopen("CON", "r", stdin);
    freopen("CON", "w", stdout);
    printf("Hello World\n");
    scanf("%d%d", &a,&b);

    return 0;
}

View Code

 

It should be noted, in fact, there is not really close, just redirects again, back to the console.

After windows / DOS, file read freopen ( " CON ",  " r " , stdin), after writing a file freopen ( " CON ",  " w " , stdout).

In linux, console devices is / dev / console: freopen ( "/ dev / console", "r", stdin).