ioctl(2) can't gets the window' size from a pty-shell' child

[adjivas]

Hello @hibariya! Today, I report this:

According to the documentation I have executed a default bash' shell.

When I request the window size's information from this shell, I get the default values.

> echo -e "lines\ncols" | tput -S
24
80

When I request the window size's information from a sub-program of shell, I get a empty structure winsize.

> ./size
winsize: [0; 0]
> echo $? # ioctl(2) hasn't occurred an error.
0

The code source used for this example is:

#include <sys/ioctl.h>
#include <stdio.h>

int main(void)
{
        struct winsize winsz;

        if (ioctl(0, TIOCGWINSZ, &winsz) != 0)
        {
                return -1;
        }
        printf("winsize: [%d; %d]\n", winsz.ws_row, winsz.ws_col);
        return 0;
}

I will more investigate later.