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 1000my effective user id is 1000My real group id is 1000My 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 0I 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 5467I 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=5517I 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: 0i:1 process ID: 5604 parent ID: 1 child ID: 0i:2 process ID: 5605 parent ID: 1 child ID: 0i: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 resultsint 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。
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本文转自被遗忘的博客园博客，原文链接：http://www.cnblogs.com/rollenholt/archive/2012/06/02/2532001.html，如需转载请自行联系原作者