プロセス制御Linux C fork()execl()exit()wait()

プロセス制御実験:
linuxの下でc言語を使用してfork(),execl(),exit(),wait()をシステム呼び出します.
[b]fork()はプロセスをコピーするために使用される[/b]
int fork() turns a single process into 2 identical processes, known as the parent and the child. On success, fork() returns 0 to the child process and returns the process ID of the child process to the parent process. On failure, fork() returns -1 to the parent process, sets errno to indicate the error, and no child process is created.
[b]execl()外部コマンドを呼び出す[/b]
execl stands for execute and leave which means that a process will get executed and then terminated by execl.
[b]exit()[/b]
int exit(int status) - terminates the process which calls this function and returns the exit status value. Both UNIX and C (forked) programs can read the status value.
[b]wait()サブプロセスの実行終了を待つ[/b]
int wait (int *status_location) - will force a parent process to wait for a child process to stop or terminate. wait() return the pid of the child or -1 for an error. The exit status of the child is returned to status_location.

#include 
#include 
#include 

int main() {
        printf("main");
        pid_t pid;
        pid = fork();
        // son process create here, exact copy from parent process
        // son process will execute the main funciton after parent process
        if(pid<0) {
                printf("return");
                return 0;
        }
        if(pid==0) {
                printf("I am the child, my pid is %d
", getpid());
        }else {
                printf("I am the parent, my pid is %d, my child pid is%d
", getpid(), pid);
        }
//      sleep(6);
}

#define _GNU_SOURCE
#include 
#include 
#include 
#include 

void main() {
//	execl("/bin/echo", "echo", "I am in execl", (char*)0);
	pid_t pid;
	int status = -10;
	pid=fork();
	if(pid==0) {
		printf("i am in son proc
");
		printf("pid = %d
", getpid());
		int t = wait(&status);
		printf("t = %d
", t);
		printf("status = %d
", status);
	//          ，wait  -1，status    
		sleep(3);
	}else {	
	//wait(&status)       pid， status   exit(5)    
	//     5， WEXITSTATUS(status)    5
	//	sleep(3);
	// wait()          ，           
		printf("i am in father proc
");
       		int t = wait(&status);
		printf("t = %d
", t);
		printf("status = %d
", status);
		printf("WEXITSTATUS(status)=%d
",WEXITSTATUS(status));
	}
	exit(5);
}