c - C中两个函数之间的指针

Question

int mqtt_connection()
{
    mqtt_broker_handle_t *broker = mqtt_connect(client_name, ip_addr, port);

    if(broker == 0) {  
    printf("Connection failed, Please check the IP and port of broker\n");  
     return 0;          
        }
    else {
        printf("Connection established successfully\n");
    }
    return 1;
}


int publish_mqtt()
{
    char msg[128] = "Test 2";

    if(mqtt_publish(broker, topic1, msg, QoS1) == -1) 
    {
            printf("publish failed\n");
    }
    else {
        printf("Sent messages\n");
    }
    return(0);
}

我在使用 scons 构建时遇到错误

master.c: In function 'publish_mqtt':
master.c:39:17: error: 'broker' undeclared (first use in this function)
if(mqtt_publish(broker, topic1, msg, QoS1) == -1) 
             ^
master.c:39:17: note: each undeclared identifier is reported only once          for each function it appears in
 scons: *** [master.o] Error 1
  scons: building terminated because of errors.

如何在两个函数之间交换 broker 的值？。还有其他方法可以实现吗？

Answer 1

How to exchange the value of broker between two functions?. Is there any other way to implement this?.

更改两个函数的签名。

1. 将第一个函数更改为返回 broker。
2. 将第二个函数更改为期望 broker 作为参数。

---

mqtt_broker_handle_t* mqtt_connection()
{
   mqtt_broker_handle_t *broker = mqtt_connect(client_name, ip_addr, port);

   if(broker == 0)
   {
      printf("Connection failed, Please check the IP and port of broker\n");  
      return NULL;          
   }
   else
   {
      printf("Connection established successfully\n");
      return broker;
   }
}


int publish_mqtt(mqtt_broker_handle_t* broker)
{
   char msg[128] = "Test 2";

   if(mqtt_publish(broker, topic1, msg, QoS1) == -1) 
   {
      printf("publish failed\n");
   }
   else
   {
      printf("Sent messages\n");
   }
   return(0);
}

---

更改调用函数。

mqtt_broker_handle_t* broker = mqtt_connection();
publish_mqtt(broker);