编辑：问题是scanf（以及我在这里尝试的其他功能）没有等待输入，程序也没有暂停。
在Mac上的Virtual Box上使用Ubuntu 18我正在使用POSIX编写服务器/客户端。我无法在client.c中读取键盘输入。
char action_type[1]; printf("Chose action: T to request time, S to shut down\n"); scanf(" %c",action_type); printf("%s", action_type);如果我在main.c中输入与第一件事相同的代码，它将正常工作。
服务器/客户端和公用程序的完整代码是：
服务器
#include <stdio.h> #include "mqueue.h" #include "commons.h" #include "errno.h" #include "stdlib.h" #include <string.h> #include <time.h> int status_closing = 0; void send_time(char* clients_pid); void send_activation(char* clients_pid); //VARIABLES related to SERVERS QUEUE mqd_t server; // server struct mq_attr servers_attributes; // server creation attributes struct mq_attr receiving_attributes; // server receiving attributes // set up attributes void set_servers_attributes(){ // set up server's attributes servers_attributes.mq_maxmsg = QUEUE_SIZE; servers_attributes.mq_msgsize = MESSAGE_SIZE; printf("attributes set \n"); }; // open server void open_servers_queue() { server = mq_open (servers_path, O_CREAT | O_RDWR | O_EXCL , 0666, &servers_attributes); if (server == -1) { printf("failed to open server's queue\n"); printf(errno); exit(-1); } else { printf("opened servers queue as: %d\n",server); } }; // check attributes void check_attributes(){ if ((mq_getattr(server,&receiving_attributes)) == -1) { printf("cannot read server's queue\n exit \n"); exit(-1); } }; void close_and_unlink_queue(){ printf("At exit closing and unlinking queue\n"); mq_close(server); mq_unlink(servers_path); }; int check_for_messages_in_the_queue(){ //printf("checking for messages\n"); int messages_in_queue; messages_in_queue = receiving_attributes.mq_curmsgs; //printf("there are %d message in the servers queue\n",messages_in_queue); // printf("message in the queue!\n"); return messages_in_queue; }; char* receive_message(){ char *receiving_buffer = malloc(sizeof(char)*MESSAGE_SIZE); if ((mq_receive(server,receiving_buffer,MESSAGE_SIZE,NULL))>0){ return receiving_buffer; } else { printf("Server failed to receive message"); mq_close(server); mq_unlink(servers_path); exit(-1); } }; void respond(char *message_type, char* clients_pid) { printf("responding\n"); char* type_one = "1"; char* type_two = "2"; char *type_three ="3"; if (strcmp(message_type, type_one) == 0) { printf("TYPE 1\n"); send_activation(clients_pid); } if (strcmp(message_type, type_two) == 0) { printf("TYPE 2\n"); send_time(clients_pid); } if (strcmp(message_type, type_three) == 0) { printf("type 3 - SHUTDOWN INITIATED\n"); } } void send_time(char* clients_pid) { time_t mytime = time(NULL); char *time_str = ctime(&mytime); time_str[strlen(time_str)-1] = '\0'; char *clientpath[20]; int clients_pid_int = atoi(clients_pid); sprintf(clientpath,"/%d",clients_pid_int); printf("clients path: %s\n",clientpath); mqd_t client; client = mq_open(clientpath,O_RDWR , 0666, &servers_attributes); if (client == -1) { printf("failes opening client's queue \n"); exit(-1); } else { printf("connected to client's queue: %d\n",client); } }; void send_activation(char* clients_pid) { char *clientpath[20]; int clients_pid_int = atoi(clients_pid); sprintf(clientpath,"/%d",clients_pid_int); printf("clients path: %s\n",clientpath); mqd_t client; client = mq_open(clientpath,O_RDWR , 0666, &servers_attributes); if (client == -1) { printf("failes opening client's queue \n"); exit(-1); } else { printf("connected to client's queue: %d\n",client); char* activation = malloc(sizeof(char)*MESSAGE_SIZE); char* activation_literal = "activation"; sprintf(activation,"%s",activation_literal); int message_sent = mq_send(client,activation,MESSAGE_SIZE,0); printf("message sent with: %d",message_sent); } }; int main() { // clean remainings of previous trials mq_close(server); mq_unlink(servers_path); // define atexit behaviour atexit(close_and_unlink_queue); //set servers attributes: set_servers_attributes(); // open server's queue open_servers_queue(); // receiving messages in the loop int condition = 1; while (1) { check_attributes(); if (check_for_messages_in_the_queue() > 0) { char *received_message = receive_message(); char *tok_one = strtok(received_message," "); char *tok_two = strtok(NULL, " "); //int clients_pid = atoi(tok_two); respond(tok_one,tok_two); } else if ((check_for_messages_in_the_queue() ==0) && (status_closing == 1)) { printf("Server's queue is empty - work finished. closing down\n"); exit(0); } } printf("Hello, World!\n"); return 0; }客户
#include <stdio.h> #include <mqueue.h> #include <unistd.h> #include "commons.h" #include <stdlib.h> #include <errno.h> #include <string.h> mqd_t client; mqd_t server; char clientpath[20]; char* sending_buffer[MESSAGE_SIZE]; struct mq_attr clients_attributes; struct mq_attr receiving_attributes; void connect_to_server(){ server = mq_open(servers_path,O_WRONLY); if(server == -1) { printf("connection to server failed\n"); } else { printf("connected to server with id: %d \n",server); } }; void set_clients_attributes(){ // deal with attributes clients_attributes.mq_maxmsg = QUEUE_SIZE; clients_attributes.mq_msgsize = MESSAGE_SIZE; }; void create_clients_queue(){ // create clients path pid_t client_pid = getpid(); sprintf(clientpath, "/%d", client_pid); // open clients queue client = mq_open(clientpath,O_RDONLY | O_CREAT | O_EXCL, 0666, &clients_attributes); // printf(errno); if (client == -1) { printf("failes opening client's queue \n"); exit(-1); } else { printf("connected to client's queue: %d\n",client); } }; void register_at_server(){ message message; message.mtype = 1; int client_pid = getpid(); message.sender = client_pid; char separator = ' '; snprintf(sending_buffer,MESSAGE_SIZE,"%ld%c%d",message.mtype,separator,message.sender); if ((mq_send(server,sending_buffer, MESSAGE_SIZE,0)) == -1) { printf("failed to send registration request\n"); exit(-1); } else { printf("%s",sending_buffer); printf("sent registration request\n"); } }; void close_and_unlink_queue(){ printf("At exit closing and unlinking queue\n"); mq_close(client); mq_unlink(clientpath); }; void check_attributes(){ if ((mq_getattr(client,&receiving_attributes)) == -1) { printf("cannot read own's queue\n exit \n"); exit(-1); } }; int check_for_messages_in_the_queue(){ //printf("checking for messages\n"); int messages_in_queue; messages_in_queue = receiving_attributes.mq_curmsgs; //printf("there are %d message in the servers queue\n",messages_in_queue); // printf("message in the queue!\n"); return messages_in_queue; }; char* receive_message(){ char *receiving_buffer = malloc(sizeof(char)*MESSAGE_SIZE); if ((mq_receive(client,receiving_buffer,MESSAGE_SIZE,NULL))>0){ return receiving_buffer; } else { printf("Server failed to receive message"); mq_close(client); mq_unlink(clientpath); exit(-1); } }; void choose_action(){ char action_type[1]; printf("Chose action: T to request time, S to shut down\n"); scanf(" %c",action_type); printf("%s", action_type); }; int main() { mq_close(client); mq_unlink(clientpath); connect_to_server(); set_clients_attributes(); create_clients_queue(); register_at_server(); int condition = 1; int client_active = 0; while (condition) { check_attributes(); if (check_for_messages_in_the_queue() > 0) { char *received_message = receive_message(); if ((strcmp(received_message, "activation")) == 0) { client_active = 1; condition = 0; free(received_message); } } } char action_type[1]; printf("Chose action: T to request time, S to shut down\n"); scanf(" %c",action_type); printf("%s", action_type); printf("Hello, World!\n"); return 0; }普通
#ifndef SERVER_COMMONS_H
#define SERVER_COMMONS_H
#include <signal.h>
// define values of server queue attributes
//define message struct
typedef struct messgae {
char content[4096];
pid_t sender;
long mtype;
} message;
#define QUEUE_SIZE 10
#define MESSAGE_SIZE sizeof(message)
// define servers path
const char servers_path[] = "/server";
#endif //SERVER_COMMONS_H
``
编辑：问题是scanf（以及我在这里尝试的其他功能）没有等待输入，程序也没有暂停。在Mac上的Virtual Box上使用Ubuntu 18，我正在使用...
发生这种情况是因为缓冲区不为空，并且该函数从其中读取了该缓冲区。要清空缓冲区，只需尝试以下代码：