通过带有stdin和stdout的dup2（）将read（）write（）写入pipe（）

Question

I need to simulate the Linux command " cal -3 ", which displays the calendar for 3 months side by side. What I need right now is to get my implementation, using pipes, working. I've been told that I can't use fork() , but rather I should use dup2() , write() , read() and close() to call system("myCustomCommand") three times. Right now my program does not display the calendar side by side.

I am trying to use pipes and ran into a problem. Here is what I am trying:

int pfd[2];
int p; //for pipe
int d; //for dup2
const int BSIZE = 256;
char buf[BSIZE];

p = pipe(pfd);
if (p == -1) { perror("pipe"); exit(EXIT_FAILURE); }
if (p == 0)
{
    d = dup2(pfd[1], 0);
    close(pfd[1]);
    nbytes = read (pfd[1], buf , BSIZE);
    close(pfd[0]);
    exit(EXIT_SUCCESS);
}
else
{
    close(pfd[0]);
    write(pfd[1], "test\n", BSIZE);
    close(pfd[1]);
    exit(EXIT_SUCCESS);
}

Unfortunately, this code does not display anything. Could you please help me out with this?

Answer 1

This looks like homework, so I'll give you a way to approach the problem:

1. Get it working with one calendar, reading in one line at a time and writing to stdout.
2. Now store each line in an array of strings, and print out each line once you get the whole calendar read in.
3. Get it working with three calendars, storing the results of each into three separate arrays of strings, then printing out all three (not next to each other).
4. Instead of printing out all of the lines from one calendar, then all of the lines from the next calendar, etc., print out the first line from each calendar, then the second line from each calendar, etc.
5. Fiddle around with the formatting until it looks right.

Answer 2

Displaying three calendars at once has nothing to do with forking processes and really you don't need to get in to pipes and stuff.

What you want to use is the ncurses library to do special control of your output.

Answer 3

Why not using FILE *fp = popen("my command", "r"); , reading the output into an array of strings, repeating that three times and concatenating arrays properly?