代碼如下，使用了共享內(nèi)存，但是子線程的代碼執(zhí)行了兩次，不明白為什么#include?<stdio.h> #include?<sys/types.h> #include?<unistd.h> #include?<sys/ipc.h> #include?<sys/shm.h> #include?<sys/wait.h> #include?<stdlib.h> //#include?<sys/signal.h> //#include?<stdlib.h> int?main() { ????key_t?key; ????key?=?ftok("/tmp",?55); ????int?size?=?getpagesize(); ????int?shmid?=?shmget(key,?size,?IPC_CREAT|00777); ????if(shmid?<?0) ????{ ????????printf("shmget?error\n"); ????????return?-1; ????} ????int?*p?=?(int?*)shmat(shmid,?NULL,?0); ????*p?=?1; ????printf("\nopration?*p=1\nthis?is?father:?*p=1=%d\n",?*p); ????pid_t?pid?=?fork(); ????if(pid?==?0); ????{ ????????int?*sp?=?(int?*)shmat(shmid,?NULL,?0); ????????*sp?=?5; ????????printf("\nopration?*sp=5\nthis?is?son:?*sp=5=%d\n",?*sp); ????????printf("this?is?son:?*p=1=%d\n",?*p); ????} ????wait(NULL); ????return?0; }輸出結(jié)果如下：opration?*p=1 this?is?father:?*p=1=1 opration?*sp=5 this?is?son:?*sp=5=5 this?is?son:?*p=1=5 opration?*sp=5 this?is?son:?*sp=5=5 this?is?son:?*p=1=5