callexec.c

进程和线程的代码

#include <unistd.h>
#include <stdarg.h>
#include <time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>

int tprintf (const char*fmt, ...);

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

 if (pid == 0)  //child process
 { sleep(5);
   tprintf("Hello from Child Process!\n");
   tprintf("I am calling exec.\n");
   execl("/bin/ps", "-a" , NULL);   
//   execl("/bin/ls", "-l" , "/etc", NULL);   
   tprintf("You should never see this because the child is already gone.\n");
 }
 else if (pid != -1)  //parent process
 { tprintf("Hello from Parent, pid %d.\n", getpid());
   sleep(1);
   tprintf("Parent forked process %d.\n", pid);
   sleep(1);
   tprintf("Parent is waiting for child to exit.\n");
   waitpid(pid, NULL, 0);
   tprintf("Parent had exited.\n");
 }
 else  tprintf(" Everything was done without error.\n");
 
return 0;
}


int tprintf (const char*fmt, ...)
{ va_list args;
	struct tm *tstruct;
	time_t tsec;
	tsec = time(NULL);
	tstruct = localtime (&tsec);
	printf("%02d:%02d:%02d: %5d|", tstruct->tm_hour, tstruct->tm_min, tstruct->tm_sec, getpid());
	va_start(args, fmt);
	return vprintf(fmt, args);
}