c - 为什么 fprintf 开始乱序打印或根本不打印？

Question

这段代码应该取一个整数，创建管道，生成两个 child ，等到他们死了，然后重新开始。但是，在循环的第三次左右，我失去了输入数字的提示，并且不再打印我输入的数字。有什么想法吗？

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

#define WRITE   1
#define READ    0

int main (int argc, const char * argv[]) {

    //Pipe file-descriptor array
    unsigned int isChildA = 0;
    int pipeA[2];
    int pipeB[2];
    int num = 0;

    while(1){


    fprintf(stderr,"Enter an integer: ");
    scanf("%i", &num);

    if(num == 0){
        fprintf(stderr,"You entered zero, exiting...\n");
        exit(0);
    }

    //Open Pipes
    if(pipe(pipeA) < 0){
        fprintf(stderr,"Could not create pipe A.\n");
        exit(1);
    }

    if(pipe(pipeB) < 0){
        fprintf(stderr,"Could not create pipe B.\n");
        exit(1);
    }

    fprintf(stderr,"Value read: %i \n", num);
    fprintf(stderr,"Parent PID: %i\n", getpid());

    pid_t procID = fork();

    switch (procID) {
        case -1:
            fprintf(stderr,"Fork error, quitting...\n");
            exit(1);
            break;

        case 0:
            isChildA = 1;
            break;

        default:
            procID = fork();

            if (procID<0) {
                fprintf(stderr,"Fork error, quitting...\n");
                exit(1);
            }
            else if(procID == 0){
                isChildA = 0;
            }

            else {

                write(pipeA[WRITE], &num, sizeof(int));
                close(pipeA[WRITE]);
                close(pipeA[READ]);
                close(pipeB[WRITE]);
                close(pipeB[READ]);

                pid_t pid;

                while (pid = waitpid(-1, NULL, 0)) {
                    if (errno == ECHILD) {
                        break;
                    }
                }

            }


            break;
    }

    if (procID == 0) {
        //We're a child, do kid-stuff.
        ssize_t bytesRead = 0;
        int response;

        while (1) {

            while (bytesRead == 0) {
                bytesRead = read((isChildA?pipeA[READ]:pipeB[READ]), &response, sizeof(int));
            }
            if (response < 2) {
                //Kill other child and self
                fprintf(stderr, "Terminating PROCID: %i\n", getpid());
                write((isChildA?pipeB[WRITE]:pipeA[WRITE]), &response, sizeof(int));
                close(pipeA[WRITE]);
                close(pipeA[READ]);
                close(pipeB[WRITE]);
                close(pipeB[READ]);
                return 0;
            }
            else if(!(response%2)){
                //Even
                response/=2;
                fprintf(stderr,"PROCID: %i, VALUE: %i\n", getpid(), response);
                write((isChildA?pipeB[WRITE]:pipeA[WRITE]), &response, sizeof(int));
                bytesRead = 0;
            }

            else {
                //Odd
                response*=3;
                response++;
                fprintf(stderr,"PROCID: %i, VALUE: %i\n", getpid(), response);
                write((isChildA?pipeB[WRITE]:pipeA[WRITE]), &response, sizeof(int));
                bytesRead = 0;
            }


        }
    }
}

    return 0;
}

这是我得到的输出...

bash-3.00$ ./proj2 
Enter an integer: 101
Value read: 101 
Parent PID: 9379
PROCID: 9380, VALUE: 304
PROCID: 9381, VALUE: 152
PROCID: 9380, VALUE: 76
PROCID: 9381, VALUE: 38
PROCID: 9380, VALUE: 19
PROCID: 9381, VALUE: 58
PROCID: 9380, VALUE: 29
PROCID: 9381, VALUE: 88
PROCID: 9380, VALUE: 44
PROCID: 9381, VALUE: 22
PROCID: 9380, VALUE: 11
PROCID: 9381, VALUE: 34
PROCID: 9380, VALUE: 17
PROCID: 9381, VALUE: 52
PROCID: 9380, VALUE: 26
PROCID: 9381, VALUE: 13
PROCID: 9380, VALUE: 40
PROCID: 9381, VALUE: 20
PROCID: 9380, VALUE: 10
PROCID: 9381, VALUE: 5
PROCID: 9380, VALUE: 16
PROCID: 9381, VALUE: 8
PROCID: 9380, VALUE: 4
PROCID: 9381, VALUE: 2
PROCID: 9380, VALUE: 1
Terminating PROCID: 9381
Terminating PROCID: 9380
Enter an integer: 102
Value read: 102 
Parent PID: 9379
PROCID: 9386, VALUE: 51
PROCID: 9387, VALUE: 154
PROCID: 9386, VALUE: 77
PROCID: 9387, VALUE: 232
PROCID: 9386, VALUE: 116
PROCID: 9387, VALUE: 58
PROCID: 9386, VALUE: 29
PROCID: 9387, VALUE: 88
PROCID: 9386, VALUE: 44
PROCID: 9387, VALUE: 22
PROCID: 9386, VALUE: 11
PROCID: 9387, VALUE: 34
PROCID: 9386, VALUE: 17
PROCID: 9387, VALUE: 52
PROCID: 9386, VALUE: 26
PROCID: 9387, VALUE: 13
PROCID: 9386, VALUE: 40
PROCID: 9387, VALUE: 20
PROCID: 9386, VALUE: 10
PROCID: 9387, VALUE: 5
PROCID: 9386, VALUE: 16
PROCID: 9387, VALUE: 8
PROCID: 9386, VALUE: 4
PROCID: 9387, VALUE: 2
PROCID: 9386, VALUE: 1
Terminating PROCID: 9387
Terminating PROCID: 9386
Enter an integer: 104
Value read: 104 
Parent PID: 9379
Enter an integer: PROCID: 9388, VALUE: 52
PROCID: 9389, VALUE: 26
PROCID: 9388, VALUE: 13
PROCID: 9389, VALUE: 40
PROCID: 9388, VALUE: 20
PROCID: 9389, VALUE: 10
PROCID: 9388, VALUE: 5
PROCID: 9389, VALUE: 16
PROCID: 9388, VALUE: 8
PROCID: 9389, VALUE: 4
PROCID: 9388, VALUE: 2
PROCID: 9389, VALUE: 1
Terminating PROCID: 9388
Terminating PROCID: 9389
105
Value read: 105 
Parent PID: 9379
Enter an integer: PROCID: 9395, VALUE: 316
PROCID: 9396, VALUE: 158
PROCID: 9395, VALUE: 79
PROCID: 9396, VALUE: 238
PROCID: 9395, VALUE: 119
PROCID: 9396, VALUE: 358
PROCID: 9395, VALUE: 179
PROCID: 9396, VALUE: 538
PROCID: 9395, VALUE: 269
PROCID: 9396, VALUE: 808
PROCID: 9395, VALUE: 404
PROCID: 9396, VALUE: 202
PROCID: 9395, VALUE: 101
PROCID: 9396, VALUE: 304
PROCID: 9395, VALUE: 152
PROCID: 9396, VALUE: 76
PROCID: 9395, VALUE: 38
PROCID: 9396, VALUE: 19
PROCID: 9395, VALUE: 58
PROCID: 9396, VALUE: 29
PROCID: 9395, VALUE: 88
PROCID: 9396, VALUE: 44
PROCID: 9395, VALUE: 22
PROCID: 9396, VALUE: 11
PROCID: 9395, VALUE: 34
PROCID: 9396, VALUE: 17
PROCID: 9395, VALUE: 52
PROCID: 9396, VALUE: 26
PROCID: 9395, VALUE: 13
PROCID: 9396, VALUE: 40
PROCID: 9395, VALUE: 20
PROCID: 9396, VALUE: 10
PROCID: 9395, VALUE: 5
PROCID: 9396, VALUE: 16
PROCID: 9395, VALUE: 8
PROCID: 9396, VALUE: 4
PROCID: 9395, VALUE: 2
PROCID: 9396, VALUE: 1
Terminating PROCID: 9395
Terminating PROCID: 9396
105
Value read: 105 
Parent PID: 9379
Enter an integer: PROCID: 9397, VALUE: 316
PROCID: 9398, VALUE: 158
PROCID: 9397, VALUE: 79
PROCID: 9398, VALUE: 238
PROCID: 9397, VALUE: 119
PROCID: 9398, VALUE: 358
PROCID: 9397, VALUE: 179
PROCID: 9398, VALUE: 538
PROCID: 9397, VALUE: 269
PROCID: 9398, VALUE: 808
PROCID: 9397, VALUE: 404
PROCID: 9398, VALUE: 202
PROCID: 9397, VALUE: 101
PROCID: 9398, VALUE: 304
PROCID: 9397, VALUE: 152
PROCID: 9398, VALUE: 76
PROCID: 9397, VALUE: 38
PROCID: 9398, VALUE: 19
PROCID: 9397, VALUE: 58
PROCID: 9398, VALUE: 29
PROCID: 9397, VALUE: 88
PROCID: 9398, VALUE: 44
PROCID: 9397, VALUE: 22
PROCID: 9398, VALUE: 11
PROCID: 9397, VALUE: 34
PROCID: 9398, VALUE: 17
PROCID: 9397, VALUE: 52
PROCID: 9398, VALUE: 26
PROCID: 9397, VALUE: 13
PROCID: 9398, VALUE: 40
PROCID: 9397, VALUE: 20
PROCID: 9398, VALUE: 10
PROCID: 9397, VALUE: 5
PROCID: 9398, VALUE: 16
PROCID: 9397, VALUE: 8
PROCID: 9398, VALUE: 4
PROCID: 9397, VALUE: 2
PROCID: 9398, VALUE: 1
Terminating PROCID: 9397
Terminating PROCID: 9398
106
Value read: 106 
Parent PID: 9379
Enter an integer: PROCID: 9399, VALUE: 53
PROCID: 9400, VALUE: 160
PROCID: 9399, VALUE: 80
PROCID: 9400, VALUE: 40
PROCID: 9399, VALUE: 20
PROCID: 9400, VALUE: 10
PROCID: 9399, VALUE: 5
PROCID: 9400, VALUE: 16
PROCID: 9399, VALUE: 8
PROCID: 9400, VALUE: 4
PROCID: 9399, VALUE: 2
PROCID: 9400, VALUE: 1
Terminating PROCID: 9399
Terminating PROCID: 9400
^C

另一件奇怪的事情是，当从 XCode 中运行时，它表现正常。但是，当在 Solaris 或 OSX 上从 bash 运行时，它会起作用。

Answer 1

替换你的 waitpid() 并试试这个:

/*
while (pid = waitpid( -1, NULL, 0))
{
    if (errno == ECHILD)
    {
        break;
    }
}
*/

while (1)
{
    if ((pid = waitpid(-1, NULL, 0)) == -1)
    {
        if (errno == ECHILD)
            break;
    }
    else
        printf("I am %d and I am reaped  %d\n", getpid(), pid);
}