实验3-1

#include
#include
#include
#include
#include

int main(){

        pid_t childpid; /*variable to store the child's pid*/
        int retval;    /*user-provided return code for child process*/
        int status;    /*child's exit status for parent process*/

        /*create new process*/
        childpid = fork();
        if (childpid >= 0) {
                if (childpid == 0) {
                        printf("CHILD: I am the child process\n");
                        printf("CHILD: Here's my PID:  %d\n",getpid());
                        printf("CHILD: My parent's PID is %d\n",getppid());
                        printf("CHILD: The value of fork return is %d\n",childpid);
                        printf("CHILD: Sleep for 1 second...\n");
                        sleep(1);
                        printf("CHILD: Enter an exit value (0~255): ");
                        scanf(" %d",&retval);
                        printf("Child: Goodbye! \n");
                        exit(retval);             /*child exits with user-provided return code*/
               }
                else {
                        printf("PARENT: I am the parent process!\n");
                        printf("PARENT: Here's my PID: %d\n",getpid());
                        printf("PARENT: The value of my child's PID is %d\n", childpid);
                        printf("PARENT: I will now wait for my child to exit.\n");
                        wait(&status);
                        printf("PARENT: Child's exit code is %d\n",WEXITSTATUS(status));
                        printf("PARENT: Goodbye!\n");
                        exit(0);
                }

        }
        else {
                perror("fork error\n");
                exit(0);
        }

        return 0;
}