#define TIMEOUT 10000L
时间: 2024-04-06 15:27:03 浏览: 23
#define TIMEOUT 10000L是一个预处理指令,用于定义一个常量。在这个例子中,TIMEOUT被定义为10000L,表示超时时间为10000毫秒。
预处理指令是在编译之前由预处理器处理的指令。它们不是真正的代码,而是用来在编译之前进行一些文本替换或条件编译的操作。
在这个例子中,定义了一个名为TIMEOUT的常量,它的值为10000L。L表示这是一个长整型常量。在代码中使用TIMEOUT时,预处理器会将其替换为10000L。
这样做的好处是可以在代码中多次使用TIMEOUT,而不需要重复写10000L,提高了代码的可读性和维护性。
相关问题
提供一个简单的用c语言的Eclipse Paho MQTT的客户端代码
好的,以下是一个简单的 C 代码片段,用于连接到 MQTT 代理并发布消息,需要使用 Eclipse Paho MQTT C 客户端库:
```c
#include "MQTTClient.h"
#define ADDRESS "tcp://mqtt.eclipse.org:1883"
#define CLIENTID "c-sample"
#define TOPIC "test/topic"
#define PAYLOAD "Hello, World!"
#define QOS 1
#define TIMEOUT 10000L
int main(int argc, char* argv[]) {
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_deliveryToken token;
int rc;
MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
MQTTClient_connect(client, &conn_opts);
pubmsg.payload = (void*)PAYLOAD;
pubmsg.payloadlen = (int)strlen(PAYLOAD);
pubmsg.qos = QOS;
pubmsg.retained = 0;
MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
printf("Message delivered %d\n", rc);
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
return rc;
}
```
这个客户端连接到 Eclipse 的公共 MQTT 测试代理,并发布一条消息到 "test/topic" 主题。你可以根据你的实际需求进行修改。注意,需要在代码中引用 Paho MQTT C 客户端库头文件并链接该库。
使用c 编写一个mqtt 通讯协议的程序
要编写MQTT通讯协议的程序,你需要使用MQTT的C语言库。以下是使用Paho MQTT C库编写MQTT客户端的示例代码。
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#define ADDRESS "tcp://localhost:1883"
#define CLIENTID "ExampleClientPub"
#define TOPIC "MQTT Examples"
#define PAYLOAD "Hello World!"
#define QOS 1
#define TIMEOUT 10000L
int main(int argc, char* argv[])
{
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_deliveryToken token;
int rc;
MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to connect, return code %d\n", rc);
exit(-1);
}
pubmsg.payload = PAYLOAD;
pubmsg.payloadlen = strlen(PAYLOAD);
pubmsg.qos = QOS;
pubmsg.retained = 0;
MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
printf("Waiting for up to %d seconds for publication of %s\n"
"on topic %s for client with ClientID: %s\n",
(int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);
rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
printf("Message with delivery token %d delivered\n", token);
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
return rc;
}
```
这个示例程序使用TCP连接到本地主机的MQTT代理,发布一个消息到“MQTT Examples”主题,然后关闭连接。你可以修改示例程序以满足你的需求,包括订阅主题、处理接收到的消息等。