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接上層嵌入式Linux系統編程常見問題解答（一） 6：假設上一題中編譯生成可執行文件名為tme。若在另一進程中調用system("./tme")，也會運行顯示時間的程序。要求根據system函數的內部實現過程，用其它學過的函數實現與system("./tme")同樣的功能。 答案： #include #include extern char **environ; int main() { pid_t pid = fork(); if(pid > 0) { waitpid(pid, NULL, 0); } else { char *buf[] = {"./tme", NULL}; execve("./tme", buf, environ); } return 0; } 7：調用函數創建一個子進程，父進程從鍵盤讀入一個整數，然后子進程把這個整數輸出來。要求：信號是進程間通信的一種方式，本題要求利用信號知識實現，不能通過寫入文件或管道等其它方式實現。 答案： /*提示：任何整數都是由0-9這幾個位組成的，可以把它的每個位都以信號的方式發給子進程，子進程接受到它的每個位后再計算出值。但有些信號比較特殊不能捕捉處理，故這里用信號10代表數字9，信號12代表數字0，信號11代表通信結束。其它的數字與其信號值相同。因為使用到了數學庫函數pow，編譯的時候最后帶上-lm選項*/ #include #include #include #include #include #include #include #include #include void fun(int n); int main() { int a = fork(); if(a > 0) { int num; printf("Input a number:\n"); scanf("%d", &num); sleep(1); /*從低到高以信號的形式向子進程發送該整數的每個位*/ int num1 = num; do{ if(num1%10 == 9) kill(a, 10); else if(num1%10 == 0) kill(a, 12); else kill(a, num1%10); num1 = num1/10; sleep(1); }while(num1 != 0); kill(a, 11); waitpid(a, 0, 0); } else { /*對相關信號注冊捕捉處理函數*/ signal(1, fun); signal(2, fun); signal(3, fun); signal(4, fun); signal(5, fun); signal(6, fun); signal(7, fun); signal(8, fun); signal(10, fun); signal(11, fun); signal(12, fun); while(1) sleep(1); } return 0; } /*子進程收到相關信號會調用此函數，此函數用來根據各個位計算出整數的值*/ void fun(int n) { static int m, i; if(n == 10) { printf("第%d位是 9\n", i + 1); m = m + 9 * pow(10, i); i++; } else if(n == 12) { printf("第%d位是 0\n", i + 1); //m = m + 0 * pow(10, i); i++; } else if(n == 11) { printf("The number is %d\n", m); sleep(1); exit(0); } else { printf("第%d位是 %d\n", i + 1, n); m = m + n * pow(10, i); i++; } } 8：不用網絡編程，用其它的IPC方式寫一個模擬聊天過程的小程序。A進程終端下輸入消息內容，按Enter后發送消息給B進程，B進程收到消息后在終端下顯示消息內容。 B進程也能實現同樣的功能。要顯示出接收消息的時間。要能循環發送接收，如果輸入QUIT就退出。 答案： /*QQA.c*/ #include #include #include #include #include #include #include #include #define BUFFER 255 #define SIZE sizeof(struct msgbuf) void showime(); int msgid; struct msgbuf{ long mtype; char mtext[BUFFER + 1]; }; void* recv(void *p); void* send(void *p); int main() { msgid = msgget((key_t)1234, 0666 | IPC_CREAT); if(msgid == -1) { perror("msgget error!"); exit(-1); } pthread_t pthid_send, pthid_recv; pthread_create(&pthid_send, NULL, send, NULL); pthread_create(&pthid_recv, NULL, recv, NULL); pthread_join(pthid_send, NULL); pthread_join(pthid_recv, NULL); msgctl(msgid, IPC_RMID, NULL); return 0; } void showtime() { time_t tt = time(NULL); struct tm *pTm; pTm = localtime(&tt); printf("%02d-%02d",(1 + pTm->tm_mon), (pTm->tm_mday)); printf(" %02d:%02d:%02d\n",(pTm->tm_hour), (pTm->tm_min), (pTm->tm_sec)); printf(" "); } void* send(void *p) { struct msgbuf msgsend; while(1) { printf(" I say "); showtime(); memset(&msgsend, 0, SIZE); msgsend.mtype = 1; scanf("%s", msgsend.mtext); if(strcmp(msgsend.mtext, "QUIT") == 0) exit(0); else msgsnd(msgid, &msgsend, SIZE, 0); } } void* recv(void * p) { struct msgbuf msgrecv; while(1) { memset(&msgrecv, 0, SIZE); msgrcv(msgid, &msgrecv, SIZE, 2,0); if(strcmp(msgrecv.mtext, "QUIT") == 0) exit(0); else { printf(" Jim say "); showtime(); printf("%s\n", msgrecv.mtext); } } } /*QQB.c*/ #include #include #include #include #include #include #include #include #define BUFFER 255 #define SIZE sizeof(struct msgbuf) void showime(); int msgid; struct msgbuf{ long mtype; char mtext[BUFFER + 1]; }; void* recv(void *p); void* send(void *p); int main() { msgid = msgget((key_t)1234, 0666 | IPC_CREAT); if(msgid == -1) { perror("msgget error!"); exit(-1); } pthread_t pthid_send, pthid_recv; pthread_create(&pthid_send, NULL, send, NULL); pthread_create(&pthid_recv, NULL, recv, NULL); pthread_join(pthid_send, NULL); pthread_join(pthid_recv, NULL); msgctl(msgid, IPC_RMID, NULL); return 0; } void showtime() { time_t tt = time(NULL); struct tm *pTm; pTm = localtime(&tt); printf("%02d-%02d",(1 + pTm->tm_mon), (pTm->tm_mday)); printf(" %02d:%02d:%02d\n",(pTm->tm_hour), (pTm->tm_min), (pTm->tm_sec)); printf(" "); } void* send(void *p) { struct msgbuf msgsend; while(1) { printf(" I say "); showtime(); memset(&msgsend, 0, SIZE); msgsend.mtype = 2; scanf("%s", msgsend.mtext); if(strcmp(msgsend.mtext, "QUIT") == 0) exit(0); else msgsnd(msgid, &msgsend, SIZE, 0); } } void* recv(void * p) { struct msgbuf msgrecv; while(1) { memset(&msgrecv, 0, SIZE); msgrcv(msgid, &msgrecv, SIZE, 1,0); if(strcmp(msgrecv.mtext, "QUIT") == 0) exit(0); else { printf(" Lucy say "); showtime(); printf("%s\n", msgrecv.mtext); } } }深圳專業嵌入式實訓。咨詢Q754634522 |
