如何在C中使父进程恢复执行

Question

我正在使用子进程和父进程编写程序，该进程允许用户键入一串字符，然后将它们转换为全大写字母。父进程提示用户输入字符串，通过管道将其发送到子进程，然后子进程使它们全部为大写。

该程序运行正常，唯一的问题是它需要一次又一次地运行而不退出。换句话说，我需要父进程在子进程完成后继续。我尝试使用各种while（1）循环无济于事。有关如何实现这一点的任何想法？谢谢！

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

void parent(int filename);
void child(int filename);

main(int argc, char * argv[])
{
        int the_pipe[2];
        pid_t process_id;

        //create the pipe
        if (pipe(the_pipe) < 0) {
                fprintf(stderr, "PIPE FAILED!\n");
                return -1;
        }

        //fork to child process
        process_id = fork();
        if (process_id == (pid_t) 0) {          //this is the child
                close(the_pipe[1]);             //close writing end
                child(the_pipe[0]);             //call the child process
                return 0;
        }
        else if (process_id < (pid_t) 0) {
                fprintf(stderr, "FORK FAILED!\n");
                return -1;
        }
        else {                                  //this is the parent
                close(the_pipe[0]);             //close reading end
                parent(the_pipe[1]);            //call the parent process
                return 0;
        }
}

void parent(int filename)
{
        FILE * fp;
        char input_line[256];           //string for user to fill

        fp = fdopen(filename, "w");     //open file for writing

        printf(" >> ");                 //prompt the user
        fgets(input_line, 256, stdin);  //get user input
        fprintf(fp, "%s", input_line);  //write user input to file

        fclose(fp);                     //close the file
        wait();                         //wait for child process to finish
}

void child(int filename)
{
        FILE * fp;
        char string[256];               //original string from pipe
        char upper[256];                //new string (all upper-case)
        int i;                          //array index

        fp = fdopen(filename, "r");     //open file for reading
        fgets(string, 256, fp);         //get the string from the pipe

        for (i = 0; i < 256; i++) {     //turn all lower-case to upper-case
                if ((string[i] > 96) && (string[i] < 123))
                        upper[i] = string[i] - 32;
                else
                        upper[i] = string[i];
        }
        printf("    %s", upper);        //print out the new string

        fclose(fp);                     //close the file
}