fork()和exec()之间有什么区别（） _fork和exec

每个应用程序(程序)都通过过程来执行, 处理是程序的运行实例。流程是通过不同的系统调用创建的, 最受欢迎的是fork()和exec()
fork()

pid_t pid = fork();

fork()通过复制调用过程来创建一个新过程, 该新过程称为子进程, 与父进程完全相同, 称为父进程, 但以下各项除外：

该子项具有其自己的唯一进程ID, 并且此PID与任何现有进程组的ID不匹配。
子级的父进程ID与父级的进程ID相同。
子级不会继承其父级的内存锁和信号量调整。
子级不会从其父级继承未完成的异步I / O操作, 也不会从其父级继承任何异步I / O上下文。

fork()的返回值
成功后, 将在父级中返回子进程的PID, 在子级中返回0。如果失败, 则在父级中返回-1, 不创建任何子级进程, 并适当设置errno。
有关fork系统调用的详细文章
exec()
exec()系列函数取代当前过程映像和新过程映像。它将程序加载到当前进程空间并从入口点运行它。
exec()系列包含以下功能, 我已经实现了execv()在下面的C程序中, 你可以尝试休息作为练习

int execl(const char *path, const char *arg, ...); int execlp(const char *file, const char *arg, ...); int execle(const char *path, const char *arg, ..., char * const envp[]); int execv(const char *path, char *const argv[]); int execvp(const char *file, char *const argv[]); int execvpe(const char *file, char *const argv[], char *const envp[]);

fork vs exec

fork启动一个新进程, 该进程是调用它的进程的副本, 而exec用另一个(不同的)进程映像替换当前进程映像。
在fork()的情况下, 父进程和子进程都同时执行, 而Control绝不会返回到原始程序, 除非有exec()错误。

//C program to illustrateuse of fork() & //exec() system call for process creation#include < stdio.h> #include < sys/types.h> #include < unistd.h> #include < stdlib.h> #include < errno.h> #include < sys/wait.h> int main(){ pid_tpid; int ret = 1; int status; pid = fork(); if (pid == -1){//pid == -1 means error occured printf ( "can't fork, error occured\n" ); exit (EXIT_FAILURE); } else if (pid == 0){//pid == 0 means child process created //getpid() returns process id of calling process //Here It will return process id of child process printf ( "child process, pid = %u\n" , getpid()); //Here It will return Parent of child Process means Parent process it self printf ( "parent of child process, pid = %u\n" , getppid()); //the argv list first argument should point to //filename associated with file being executed //the array pointer must be terminated by NULL //pointer char * argv_list[] = { "ls" , "-lart" , "/home" , NULL}; //the execv() only return if error occured. //The return value is -1 execv( "ls" , argv_list); exit (0); } else { //a positive number is returned for the pid of //parent process //getppid() returns process id of parent of //calling process //Here It will return parent of parent process's ID printf ( "Parent Of parent process, pid = %u\n" , getppid()); printf ( "parent process, pid = %u\n" , getpid()); //the parent process calls waitpid() on the child //waitpid() system call suspends execution of //calling process until a child specified by pid //argument has changed state //see wait() man page for all the flags or options //used here if (waitpid(pid, & status, 0)> 0) {if (WIFEXITED(status) & & !WEXITSTATUS(status)) printf ( "program execution successful\n" ); else if (WIFEXITED(status) & & WEXITSTATUS(status)) { if (WEXITSTATUS(status) == 127) {//execv failed printf ( "execv failed\n" ); } else printf ( "program terminated normally, " " but returned a non-zero status\n" ); } else printf ( "program didn't terminate normally\n" ); } else { //waitpid() failed printf ( "waitpid() failed\n" ); } exit (0); } return 0; }

输出如下：