I'm writing a program in C for Linux. I plan on using popen() to run another program. While I'm waiting for that program to finish, I want to be able to detect if the user presses keys on the keyboard so I know if they want to continue processing their files or if they want to pause after pclose(). What is the best way to accomplish this?

CodePudding user response：

You can use two threads, one thread running the popen commmand while the other thread is waiting for a key, join the first thread and then check if any key was pressed, then pclose and cancel the thread waiting for a key. An example using C (it is trivial to adapt it to C ), I'm ommiting error checks for brevity:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

FILE *popen(const char *, const char *);
int pclose(FILE *);

static int key;

void *handle_cmd(void *arg)
{
    FILE *cmd = arg;
    char result[1024];

    while (fgets(result, sizeof(result), cmd))
    {
        printf("%s", result);
    }
    return NULL;
}

void *handle_key(void *arg)
{
    (void)arg;
    key = getchar();
    return NULL;
}

int main(void)
{
    // Simulate a long read using sleep 5
    // to give you enough time to press a key   enter
    FILE *cmd = popen("sleep 5; echo 'command finished'", "r");
    pthread_t th_cmd, th_key;

    pthread_create(&th_cmd, NULL, handle_cmd, cmd);
    pthread_create(&th_key, NULL, handle_key, NULL);
    pthread_join(th_cmd, NULL);
    if (key != 0)
    {
        printf("%c was pressed\n", key);
    }
    pclose(cmd);
    pthread_cancel(th_key);
    return 0;
}