IO流在fork()的ed进程中

The following example code executes, but output from the forked process is not readable: nothing is shown on console until I press enter, and then "Read failed!" shows.

下面的示例代码执行，但是来自分叉进程的输出不可读:在我按enter之前，控制台上没有显示任何内容，然后显示“Read failed!”

The question is: why is that, and how can I interact with stdin and stdout from the fork()'ed process?

问题是:为什么会这样，以及如何从fork()的ed过程与stdin和stdout进行交互?

/* example1.c */

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main() {
    pid_t pid = fork();

    if (!pid) {
        // child

        char s[64];
        printf("Enter something: ");
        char *res = fgets(s, 64, stdin);
        if (!res) {
            printf("Read failed!\n");
        } else {
            printf("You entered: %s", s);
        }
    }

    return 0;
}

Update:

更新:

Another example of strange behavior of IO streams:

另一个关于IO流的奇怪行为的例子:

/* example2.c */

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main() {
    pid_t pid = fork();

    if (!pid) {
        // child

        char *argv[] = {
            "-c",
            "/home/user/echo.sh",
            NULL
        };

        execv("/bin/sh", argv);
    }
    return 0;
}

echo.sh script:

的回声。sh脚本:

#!/bin/sh

read -p "Enter something: " INPUT
echo "You entered $INPUT"

This one returns

这一个回报

Enter something: /home/user/echo.sh: line 3: read: read error: 0: Input/output error
You entered

Update 2:

更新2:

Looks like this code does exactly what's needed:

看起来这段代码所做的正是我们所需要的:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main() {
    pid_t pid = vfork();
    if (!pid) {
        // child
        system("/home/user/echo.sh");
    }
    return 0;
}

The solution was to replace fork with vfork. I just don't know why is this one working...

解决方案是用vfork替换fork。我只是不知道为什么这个工作…

3 个解决方案

#1

I think you want wait(2). As in

我想你需要等一下。就像在

/* example1.c */

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main() {
    int status;
    pid_t pid = fork();

    if (!pid) {
        // child

        char s[64];
        printf("Enter something: ");
        char *res = fgets(s, 64, stdin);
        if (!res) {
            printf("Read failed!\n");
        } else {
            printf("You entered: %s", s);
        }
    }
    else
    {
        while (wait(&status) != pid);
    }
    return 0;
}

3 个解决方案

#1

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