[SOLVED] Problem when redirecting standard output with dup and dup2 in c

Problem when redirecting standard output with dup and dup2 in c

I have a problem with dup and dup2.

int copy (char * file1, char * file2) {
        int dr = open(file1, O_RDONLY);
        if (dr == -1) {
                return -1;
        }

        int dw = open(file2, O_WRONLY|O_TRUNC|O_CREAT, 0644); 
        if (dw == -1) {
                return -1;
        }

        int save0 = dup(0); 
        int save1 = dup(1); 

        dup2(dr, 0); 
        close(dr); 

        dup2(dw, 1); 
        close(dw); 

        char c;
        while ((c = getchar()) != EOF) {  
                putchar(c); 
        }

        dup2(save0, 0); 
        dup2(save1, 1); 

        printf("Hi");
        return 0;
}

I don't understand why the data from my file file1 is displayed on the screen because dr is standard input and dw is standard output...

Thanks for the help.

Solution

You (probably) just need to flush the buffers:

while ((c = getchar()) != EOF) {  
        putchar(c); 
}
fflush(stdout);   /* Actually write to the file */
dup2(save0, 0); 
dup2(save1, 1);

Since you haven't included the full code, it's hard to be certain. Also, make sure you haven't done any read-like functions (eg fread, fgetc, etc) on stdin before this function is called.