enter SIGTSTP signal in child process, different child process behaves differently?

I'm implement my own shell on MAC, in my own shell, when I enter "Control+Z" or "Control+C", it should ignores them. but when running the command such as "sleep 10" or "cat". It behaves as default.

However, in my implementation, it behaves weird.

void sig_handler(int signo) {
    if (signo == SIGINT || signo == SIGQUIT || signo == SIGTSTP)  {
       // ignores
    } else {
        // other signals, behaves default
        signal(signo, SIG_DFL);
        raise(signo);
    }
}

int main() {
    
    signal(SIGINT, sig_handler);
    signal(SIGTSTP, sig_handler);
    signal(SIGQUIT, sig_handler);

    while (1){
         printf(">> ");
         fflush(stdout);
          
         //parse the input; skip the code for simplicity
         cmd = parse_input();
         // for example, cmd = {"cat", NULL}; or cmd = {"sleep", "60", NULL}, or cmd = {"ls", NULL}

            pid_t child_pid;
            pid = fork();
            if (pid < 0) {
                perror("error:fork");
                exit(EXIT_FAILURE);
            }
            if (pid == 0) {
                child_pid = pid;
                execvp(cmds[0][0], cmds[0]);
                perror("error:exe");
                exit(EXIT_FAILURE);
            } else {
                int status;
                waitpid(child_pid, &status, WUNTRACED | WCONTINUED);
            }
         
    }

}

when I run the program with the following user input, it displays as follows

>> cat
^Z>> ls

>> 

I first enter cat, then enter control+Z, the terminal goes back to waiting for use enter prompt. But when enter ls next, it supposed to list all files in current directory, but it just shows a newline, and when I hit "return again, it goes back to waiting for user to enter prompt. Only then, it seems back to normal shell prompt.

>> sleep 10
^Z>> ls
file1 file2 fil3
>>

instead of cat, we use sleep, the program seems handle "control+Z" as expected .

Any help

From the documentation of signals:

> During an execve(2), the dispositions of
handled signals are reset to the default; the dispositions of
ignored signals are left unchanged.

Since you're handling these signals with the sig_handler() function, they get reset to the default disposition when you do execvp(cmds[0][0], cmds[0]);. (How could it make sense not to reset them, since the function doesn't exist in the cat and ls programs?)

So you should ignore them, not handle them:

    signal(SIGINT, SIG_IGN);
    signal(SIGTSTP, SIG_IGN);
    signal(SIGQUIT, SIG_IGN);