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Linux不同进程拥有独立的虚拟地址空间。即使是父子进程也是如此。
当父进程创建一个子进程时，子进程会复制父进程地址空间中的大部分数据资源，包括代码段、变量和文件描述符等（采用写时复制机制）。
因此会有下面有趣的现象，
#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include
<wait.h> int main() { char buffer[64] = {0}; //创建子线程 pid_t pid = fork(); if
(pid == -1) { perror("fork"); return -1; } if (pid == 0) { sleep(5);
printf("The address of buffer in child is: %p.\n", buffer); printf("The
buffer[0] is: %c\n", buffer[0]); } else { printf("The address of buffer in
parent is: %p.\n", buffer); buffer[0] = 'J'; printf("The buffer[0] is: %c\n",
buffer[0]); wait(NULL); } }
父子进程中对buffer数组首地址的打印是相同的，但是在父进程中改变buffer[0]的值，却无法影响到子进程中buffer[0]的值。
这是因为父子进程运行在完全独立的虚拟地址空间中，即使buffer的地址指向相同，但是在MMU和操作系统的共同操纵（虚拟地址映射）下，父进程的buffer和子进程的buffer指向的是不同的物理内存地址。
所以，子进程可以复用父进程的变量资源，而不用担心受到父进程的影响，因为自己拿到的是副本。
