#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
*/
<br><br>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。
