mydup2.c

mydup2.c

#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <linux/limits.h>

#define OPEN_MAX 1024

int mydup2(int filedes, int filedes2)
{
    int open_fds[OPEN_MAX];
    int open_count = 0;
    int new_fds;
    int i;
    errno = 0;
    // test wether filedes is open and a valid file descriptor
    if((open_fds[open_count++] = dup(filedes)) == -1)
        return -1;
    // test wether filedes2 is a valid file descriptor
    if(filedes2 < 0 || filedes2 > OPEN_MAX)
    {
        errno = EBADF;
        return -1;
    }
    // if equal, return directly
    if(filedes == filedes2)
    {
        return filedes;
    }
    // test wether filedes2 is open, and close it if it is open
    if((open_fds[open_count++] = dup(filedes2)) >= 0)
    {
        if(close(filedes2) == -1)
        {
            return -1;
        }
    }
    // dup until the return file descriptor equals to filedes2
    new_fds = dup(filedes);
    open_fds[open_count++] = new_fds;
    while(new_fds != -1 && new_fds != filedes2)
    {
        open_fds[open_count++] = new_fds;
        new_fds = dup(filedes);
    }
    // close the des open by dup unless the last one
    for(i = 0; i < open_count - 1; ++i)
    {
        close(open_fds[i]);
    }
    return new_fds;

}

void test_mydup2(int (*fun_dup2)(int,int))
{
    // test case
    int old_fds[] = {0, 0, 2,  0, -1,  10,    -1, 65536};
    int new_fds[] = {0, 2, 2, 30,  2,  20, 65536, 65536};
    int count =  sizeof(old_fds)/sizeof(int);
    int ret;
    int i;
    // begin test
    for(i = 0; i < count; i++)
    {
        printf("dup2(%d, %d) : ", old_fds[i], new_fds[i]);
        ret = fun_dup2(old_fds[i], new_fds[i]);
        if(-1 == ret)
        {
            printf("%s\n", strerror(errno));
        }
        else if(ret == new_fds[i])
        {
            printf("success.\n");
            if(ret != 0 && ret != 1 && ret != 2)
                close(ret);
        }
        else 
        {
            printf("failed, not equal.\n");
        }
    }
    // test: dup stdout to 20, and print a string by 20
    printf("dup(1, 20), write(20, \"A test\\n\", 7) : ");
    fflush(stdout);
    fun_dup2(1, 20);
    write(20, "A test\n", 7);
    printf("\n");
    close(20);
}

int main()
{
    // test my dup2
    printf("********* my dup2 ***********\n");
    test_mydup2(mydup2);
    // test standard dup2 for a contrast
    printf("********standard dup2********\n");
    test_mydup2(dup2);

    return 0;
}