Linux c学习进程基础学习

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

int main(int argc, char const *argv[])
{
	printf("I am process %ld\n", (long)getpid() );
	printf("My parent is %ld\n", (long)getppid());
	return 0;
}

 上面的例子输出了进程的ID和他的父进程的ID

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

int main(int argc, char const *argv[])
{
	printf("my real user id is %ld\n", (long)getuid());
	printf("my effective user id is %ld\n",(long)geteuid());
	printf("My real group id is %ld\n", (long)getgid());
	printf("My effective group id is %ld\n",(long)getegid() );
	return 0;
}
/*
this program run's result as follows :
my real user id is 1000
my effective user id is 1000
My real group id is 1000
My effective group id is 1000
*/

 上面的这个程序打印进程的各种ＩＤ和组ＩＤ

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

int main(int argc, char const *argv[])
{
	int x;
	x=0;
	fork();
	printf("I am process %ld and my x is %d\n", (long)getpid() ,x);
	return 0;
}

/*
this program run's result as follows:

I am process 5416 and my x is 0
I am process 5417 and my x is 0
*/

简单的fork的例子

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

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

	childpid=fork();
	if(childpid== -1){
		perror("Failed to fork\n");
		return 1;
	}

	if(childpid==0){
		printf("I am child %ld\n", (long)getpid());
	}else{
		printf("I am parent %ld\n",(long)getpid() );
	}
	return 0;
}
/*
this program run's result as follows:
I am parent 5467
I am child 5468

*/

 上面的例子输出了执行fork之后，父进程和子进程分别输出自身的ＩＤ

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

int main(int argc, char const *argv[])
{
	pid_t mypid;
	pid_t childpid;

	mypid=getpid();
	childpid=fork();
	if(childpid==-1){
		perror("Failed to frok\n");
		return 1;
	}

	if(childpid==0){
		// child codes
		printf("I am child %ld, ID= %ld\n",(long)getpid(),(long)mypid);
	}else{
		// parent codes
		printf("I am parent  %ld, ID=%ld\n",(long)getpid(),(long)mypid );
	}
	return 0;
}

/*
this program run's result as follows:

I am parent  5517, ID=5517
I am child 5518, ID= 5517

*/

 父进程在调用fork之前，将mypid设置为自己的进程ＩＤ，执行ｆｏｒｋ之后，子进程获得了包含所有变量在内的父进程的地址空间的一份拷贝，由于子进程没有重置ｍｙｐｉｄ，所以打印出的指不一样。

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

int main(int argc, char const *argv[])
{
	pid_t childpid=0;
	int i,n;

	/*check for vaild number of common-line arguments*/
	if(argc!=2){
		fprintf(stderr, "usage: %s process \n", argv[0] );
		return 1;
	}

	n=atoi(argv[1]);
	for ( i = 0; i < n; ++i)
	{
		if(childpid=fork()){
			break;
		}

		fprintf(stderr, "i:%d process ID: %ld parent ID: %ld child ID: %ld\n", i,
			(long)getpid(),(long)getppid(),(long)childpid);
	}
	return 0;
}

/*
this program run's result as follows:

i:0 process ID: 5603 parent ID: 1 child ID: 0
i:1 process ID: 5604 parent ID: 1 child ID: 0
i:2 process ID: 5605 parent ID: 1 child ID: 0
i:3 process ID: 5606 parent ID: 1 child ID: 0
*/

 上面的程序简单的创建了一个进程链。１－>2->3->4...，另外大家要注意我在这里使用的是stderr，而不是stdout，因为系统会对写入stdout的进行缓冲。这样，特定的消息不能在printf之后立即显示。写入stderr则不会进行缓冲，而是立即写出。

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

int main(int argc, char const *argv[])
{
	pid_t childpid=0;
	int i,n;

	if (argc!=2)
	{
		fprintf(stderr, "usage: %s processes\n",argv[0] );
		return 1;
	}

	n=atoi(argv[1]);
	for ( i = 0; i < n; ++i)
	{
		if((childpid=fork())<=0){
			break;
		}
		fprintf(stderr, "i:%d process ID:%ld, parent ID: %ld, child ID: %ld\n",
			i,(long)getpid(),(long)getppid(),(long)childpid );
	}
	return 0;
}

 上面的例子简单的创建了一个进程扇。

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

// this program will print some information after all the child process exits;

pid_t  r_wait(int* stat_lco);

int main(int argc, char const *argv[])
{
	pid_t childpid=0;
	int i,n;

	if (argc!=2)
	{
		fprintf(stderr, "usage: %s processes\n",argv[0] );
		return 1;
	}

	n=atoi(argv[1]);
	for ( i = 0; i < n; ++i)
	{
		if((childpid=fork())<=0){
			break;
		}
		while(r_wait(NULL)>0);  /*wait for all of your children*/
		fprintf(stderr, "i:%d process ID:%ld, parent ID: %ld, child ID: %ld\n",
			i,(long)getpid(),(long)getppid(),(long)childpid );
	}
	return 0;
}

pid_t  r_wait(int* stat_lco){
	int retval;
	while(((retval=wait(stat_lco)==-1)&& (errno==EINTR));
		return retval;
}

 上面的进程扇使得所有子进程都推出之后，打印消息。

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

// can you discribe all of this program run's results

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

	// set up signal handlers here

	childpid=fork();
	if(childpid==-1){
		perror("Faild to fork\n");
		return 1;
	}

	if(childpid==0){
		fprintf(stderr, "I am child %ld\n",(long)getpid() );
	}else if(wait(NULL)!=childpid){
		fprintf(stderr, "A signal must have interrupted the wait\n");
	}else{
		fprintf(stderr, "I am parent %ld with child %ld\n", (long)getpid(),(long)childpid);
	}

	
	return 0;
}

 你能描述一下上面例子的所有可能输出吗？

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <errno.h>

int main(int argc, char const *argv[])
{
	pid_t childpid=0;
	int i,n;

	if(argc!=2){
		fprintf(stderr, "Usage: %s processes\n", argv[0] );
		return 1;
	}

	n=atoi(argv[1]);
	for (i = 0; i < n; ++i)
	{	
		if((childpid=fork())<=0){
			break;
		}
		for(;;){
			childpid=wait(NULL);
			if((childpid== -1)&&(errno != EINTR)){
				break;
			}
		}
	}
	fprintf(stderr, "I am process %ld, my parent is %ld\n",(long)getpid(),(long)getppid() );
	return 0;
}

 上面的例子创建了一个进程扇，所有被创建的进程都是原始进程的子进程。

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

int main(int argc, char const *argv[])
{
	pid_t childpid;
	childpid=fork();
	if(childpid== -1){
		perror("Failed to fork\n");
		return 1;
	}				/*child code*/
	if(childpid==0){
		execl("/bin/ls","ls","-l",NULL);
		perror("child Failed to execl ls\n");
		return 1;
	}				/*parent code*/
	if(childpid!=wait(NULL)){
		perror("parent Failed to wait due to signal or error\n");
		return 1;
	}
	return 0;
}

 创建子进程来执行： ls -l命令。