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。
