Linux下进程编程.docx

写给linux编程的初学者，进程编程是linux编程首先要学习的东西，往后要学习进程之间通讯的一些编程。下面的是进程编程的一些基本函数。1 用户标识（UID）和有效用户标识（EUID）使用getuid函数和geteuid函数来获取当前进程的用户标识和有效用户标识#include #include #include int main(void) printf(Current process UID : %ldn,(long)getuid(); printf(Current porcess EUID : %ldn,(long)geteuid(); return 0; 运行结果：Current process UID:500Current process EUID:500 2. fork函数通过fork函数并判断函数返回值，根据返回值来判断是在父进程还是子进程。#include #include #include int main(void) pid_t pid;/fork函数如果返回值小于0，表示调用失败/如果返回值为0，表示处于进程中，如果大于0，表示在父进程中 if(pid=fork()0) perror(Cannot create the new process); return 1; else if(pid=0) printf(In the child process!n); return 0; else printf(In the parent process!n); return 0; 运行结果：In the child processs!In the parent process!调用fork函数后，其后代码会被父子进程分别执行。#include #include #include int main(void) fork(); printf(Will be executed twicen); return 0; 运行结果：Will be excuted twiceWill be excuted twice 3. vfork函数首先定义g_var为全局变量， var为局部变量，然后调用fork函数创建子进程，并在子进程对g_var变量和var变量进行修改。子进程在输出这两个变脸值后退出，输出父进程中的这两个变量的取值情况。#include #include #include int g_var=0;int main(void) pid_t pid; int var=1; printf(process id:%ldn,(long)getpid(); printf(before execute the fork system call, g_var=%d var=%dn,g_var,var); if(pid=fork()0) perror(Cannot create a new process); return 1; else if(pid=0) g_var+; var+; printf(process id : %ld, g_var=%d var=%dn,(long)getpid(),g_var,var); _exit(0); printf(process id : %ld, g_var=%d var=%dn,(long)getpid(),g_var,var); return 0; 运行结果：Process id :24437Before excute the fork system call,g_var=0 var=1Process id :24438, g_var=1 var=2Process id :24437, g_var=0 var=1修改上面的程序，将fork函数的语句进行替换，使用vfork函数，将代码保存并运行#include #include #include int g_var=0;int main(void) pid_t pid; int var=1; printf(process id:%ldn,(long)getpid(); printf(before execute the fork system call, g_var=%d var=%dn,g_var,var); if(pid=vfork()0) perror(Cannot create a new process); return 1; else if(pid=0) g_var+; var+; printf(process id : %ld, g_var=%d var=%dn,(long)getpid(),g_var,var); _exit(0); printf(process id : %ld, g_var=%d var=%dn,(long)getpid(),g_var,var); return 0; 运行结果：Process id :24574Before excute the fork system call,g_var=0 var=1Process id :24575, g_var=1 var=2Process id :24574, g_var=1 var=2 4 exec 函数族execvp函数支持参数列表，使用参数列表将使程序获得更大的灵活性，程序通过读取agrv中的参数，实现对输入的shell命令的执行。#include #include int main(int argc,char* argv) if(argc2) printf(Usage: %s pathn,argv0); return 1; execlp(/bin/ls,ls,argv1,(char*)NULL); return 0; 5 exit函数使用atexit注册了一个在进程退出时的处理函数，该处理函数只是显示一段文字信息。Main函数退出时将调用exit函数，这样进程就会在退出时自动调用atexit注册的处理函数。#include #include #include void do_at_exit(void) printf(You can see the output when the program terminatesn);int main() int flag; flag=atexit(do_at_exit); if (flag != 0) printf(Cannot set exit functionn); return EXIT_FAILURE; exit(EXIT_SUCCESS); 6 _exit函数下面的程序和上面的除了退出函数不同，其他都一样。不同的是使用_exit函数退出时，不会执行atexit中注册的处理函数 #include #include #include void do_at_exit(void) printf(You can see the output when the program terminatesn);int main() int flag; flag=atexit(do_at_exit); if (flag != 0) printf(Cannot set exit functionn); return EXIT_FAILURE; _exit(EXIT_SUCCESS); 7 kill 函数发送信号直接用kill函数给进程发送结束信号或是让程序自动退出。#include #include #include #include int main(int argc,char* argv) pid_t pid; int exit_code; pid=getpid(); srand(unsigned)pid); exit_code=(int)(rand() % 256); sleep(10); if(atoi(*(argv+1) % 2) printf(the child process id:%d receive signal SIGKILLn,pid); kill(pid,9); else printf(the child process id:%d normally exit,exit_code is %0xn,pid,exit_code); exit(exit_code); 下面程序通过fork函数创建子进程，并调用execl函数执行上面的程序。为了方便了解程序运行情况，在父进程中显示了创建的子进程的进程号。在while循环中调用wait函数，跳出条件是wait函数放回值小于0，或wait_pid为-1。这种情况下，所有的子进程都已经完全退出。#include #include #include #include int main(int argc,char* argv) pid_t pid,wait_pid; int status; int i; if(argc4) printf(Usage: %s para1 para2 para3n,argv0); return 1; for(i=1;i4;i+) if(pid=fork()=0) execl(./p7.14,p7.14,argvi,NULL); else printf(create the child process id: %dn,pid); while(wait_pid=wait(&status) & wait_pid!=-1) printf(process id:%d exit,exit_code is %0xn,wait_pid,status); return 0; 8 waitpid函数使用waitpid等待SIGSTOP,SIGCONT和SIGKILL这3种信号.#include #include #include #include int main(void) pid_t pid,wait_pid; int status; pid = fork(); if (pid=-1) perror(Cannot create new process); exit(1); else if (pid=0) printf(child process id: %ldn, (long) getpid(); pause(); _exit(0); else do wait_pid=waitpid(pid, &status, WUNTRACED | WCONTINUED); if (wait_pid = -1) perror(cannot using waitpid function); exit(1); if (WIFEXITED(status) printf(child process exites, status=%dn, WEXITSTATUS(status); if(WIFSIGNALED(status) printf(child process is killed by signal %dn, WTERMSIG(status); if (WIFSTOPPED(status) printf(child process is stopped by signal %dn, WSTOPSIG(status);