Software (mqtt.org)中mqtt客户端的c库里面有一个叫MQTT-C的库，就2个实现文件，算比较简单的了，实现了基本的mqtt客户端功能，移植一下试试。
我的移植代码放在我的资源里面：https://download.csdn.net/download/oushaojun2/87281533?spm=1001.2014.3001.5501
进到这个项目的github仓库地址：https://github.com/LiamBindle/MQTT-C
src里面有两个文件mqtt.c和mqtt_pal.c，第一个是mqtt的实现，第二个是移植需要的文件。移植文件里面主要包括了常见平台的socket接收和发送函数的封装，假如移植到自己的平台可能需要修改这个文件里面的代码，目前的移植是想要在visual studio里面移植，里面已经有了移植接口了。
移植到visual studio里面的步骤如下：
1 将MQTT-C的代码增加到visual studio的一个空白工程里面。需要的文件如下，记得删掉创建工程是自带的文件和修改文件包含路径：
2 修改mqtt_pal.h，128行增加一行：#pragma comment(lib,"ws2_32.lib")，为了在win32平台下链接到ws2_32.lib库，否则编译
3 修改posix_sockets.h内容，虽然这个头文件是按照socket标准接口来调用的，但是win32的socket接口跟linux的接口有些不一样，例如close在win32里面是没有的，gai_strerror在win32里面没效果，win32需要调用WSAStartup函数。修改如下：
-
#if !defined(__POSIX_SOCKET_TEMPLATE_H__)
-
#define __POSIX_SOCKET_TEMPLATE_H__
-
-
#include <stdio.h>
-
#include <sys/types.h>
-
#if !defined(WIN32)
-
#include <sys/socket.h>
-
#include <netdb.h>
-
#else
-
#include <ws2tcpip.h>
-
#define close closesocket
-
#endif
-
#if defined(__VMS)
-
#include <ioctl.h>
-
#endif
-
#include <fcntl.h>
-
-
/*
-
A template for opening a non-blocking POSIX socket.
-
*/
-
int open_nb_socket(const char* addr, const char* port);
-
-
int open_nb_socket(const char* addr, const char* port) {
-
struct
addrinfo hints = {
0};
-
-
hints.ai_family = AF_UNSPEC;
/* IPv4 or IPv6 */
-
hints.ai_socktype = SOCK_STREAM;
/* Must be TCP */
-
int sockfd =
-1;
-
int rv;
-
struct
addrinfo *p, *servinfo;
-
-
#if defined(WIN32)
-
{
-
WSADATA wsaData;
-
int iResult;
-
iResult =
WSAStartup(
MAKEWORD(
2,
2), &wsaData);
-
if (iResult != NO_ERROR) {
-
printf(
"WSAStartup failed: %d\n", iResult);
-
return
1;
-
}
-
}
-
#endif
-
-
/* get address information */
-
rv =
getaddrinfo(addr, port, &hints, &servinfo);
-
if(rv !=
0) {
-
#if defined(__UNIX__)
-
fprintf(stderr,
"Failed to open socket (getaddrinfo): %s\n",
gai_strerror(rv));
-
#else
-
fprintf(stderr,
"Failed to open socket (getaddrinfo): %s\n",
gai_strerrorA(rv));
-
#endif
-
return
-1;
-
}
-
-
/* open the first possible socket */
-
for(p = servinfo; p !=
NULL; p = p->ai_next) {
-
sockfd =
socket(p->ai_family, p->ai_socktype, p->ai_protocol);
-
if (sockfd ==
-1)
continue;
-
-
/* connect to server */
-
rv =
connect(sockfd, p->ai_addr, p->ai_addrlen);
-
if(rv ==
-1) {
-
close(sockfd);
-
sockfd =
-1;
-
continue;
-
}
-
break;
-
}
-
-
/* free servinfo */
-
freeaddrinfo(servinfo);
-
-
/* make non-blocking */
-
#if !defined(WIN32)
-
if (sockfd !=
-1)
fcntl(sockfd, F_SETFL,
fcntl(sockfd, F_GETFL) | O_NONBLOCK);
-
#else
-
if (sockfd != INVALID_SOCKET) {
-
int iMode =
1;
-
ioctlsocket(sockfd, FIONBIO, &iMode);
-
}
-
#endif
-
#if defined(__VMS)
-
/*
-
OpenVMS only partially implements fcntl. It works on file descriptors
-
but silently fails on socket descriptors. So we need to fall back on
-
to the older ioctl system to set non-blocking IO
-
*/
-
int on =
1;
-
if (sockfd !=
-1)
ioctl(sockfd, FIONBIO, &on);
-
#endif
-
-
/* return the new socket fd */
-
return sockfd;
-
}
-
-
#endif
4 修改simple_publisher.c文件，这个文件的接口都是posix接口，在win32环境下有些要修改，例如建立线程函数等。修改如下：
-
-
/**
-
* @file
-
* A simple program to that publishes the current time whenever ENTER is pressed.
-
*/
-
#if defined(__unix__)
-
#include <unistd.h>
-
#include <stdlib.h>
-
#include <stdio.h>
-
#include <pthread.h>
-
#else
-
#include <stdlib.h>
-
#include <stdio.h>
-
#pragma warning(disable : 4996)
-
#endif
-
-
#include <mqtt.h>
-
#include "posix_sockets.h"
-
-
-
/**
-
* @brief The function that would be called whenever a PUBLISH is received.
-
*
-
* @note This function is not used in this example.
-
*/
-
void publish_callback(void** unused, struct mqtt_response_publish *published);
-
-
/**
-
* @brief The client's refresher. This function triggers back-end routines to
-
* handle ingress/egress traffic to the broker.
-
*
-
* @note All this function needs to do is call \ref __mqtt_recv and
-
* \ref __mqtt_send every so often. I've picked 100 ms meaning that
-
* client ingress/egress traffic will be handled every 100 ms.
-
*/
-
#if defined(__UNIX__)
-
void* client_refresher(void* client);
-
#else
-
DWORD WINAPI client_refresher(LPVOID client);
-
#endif
-
-
-
/**
-
* @brief Safelty closes the \p sockfd and cancels the \p client_daemon before \c exit.
-
*/
-
#if defined(__unix__)
-
void exit_example(int status, int sockfd, pthread_t *client_daemon);
-
#else
-
void exit_example(int status, int sockfd, HANDLE client_daemon);
-
-
#endif
-
-
/**
-
* A simple program to that publishes the current time whenever ENTER is pressed.
-
*/
-
int main(int argc, const char *argv[])
-
{
-
const
char* addr;
-
const
char* port;
-
const
char* topic;
-
-
/* get address (argv[1] if present) */
-
if (argc >
1) {
-
addr = argv[
1];
-
}
else {
-
addr =
"test.mosquitto.org";
-
}
-
-
/* get port number (argv[2] if present) */
-
if (argc >
2) {
-
port = argv[
2];
-
}
else {
-
port =
"1883";
-
}
-
-
/* get the topic name to publish */
-
if (argc >
3) {
-
topic = argv[
3];
-
}
else {
-
topic =
"datetime";
-
}
-
-
/* open the non-blocking TCP socket (connecting to the broker) */
-
int sockfd =
open_nb_socket(addr, port);
-
-
if (sockfd ==
-1) {
-
perror(
"Failed to open socket: ");
-
exit_example(EXIT_FAILURE, sockfd,
NULL);
-
}
-
-
/* setup a client */
-
struct
mqtt_client client;
-
uint8_t sendbuf[
2048];
/* sendbuf should be large enough to hold multiple whole mqtt messages */
-
uint8_t recvbuf[
1024];
/* recvbuf should be large enough any whole mqtt message expected to be received */
-
mqtt_init(&client, sockfd, sendbuf,
sizeof(sendbuf), recvbuf,
sizeof(recvbuf), publish_callback);
-
/* Create an anonymous session */
-
const
char* client_id =
NULL;
-
/* Ensure we have a clean session */
-
uint8_t connect_flags = MQTT_CONNECT_CLEAN_SESSION;
-
/* Send connection request to the broker. */
-
mqtt_connect(&client, client_id,
NULL,
NULL,
0,
NULL,
NULL, connect_flags,
400);
-
-
/* check that we don't have any errors */
-
if (client.error != MQTT_OK) {
-
fprintf(stderr,
"error: %s\n",
mqtt_error_str(client.error));
-
exit_example(EXIT_FAILURE, sockfd,
NULL);
-
}
-
-
/* start a thread to refresh the client (handle egress and ingree client traffic) */
-
#if defined(__UNIX__)
-
pthread_t client_daemon;
-
if(
pthread_create(&client_daemon,
NULL, client_refresher, &client)) {
-
fprintf(stderr,
"Failed to start client daemon.\n");
-
exit_example(EXIT_FAILURE, sockfd,
NULL);
-
-
}
-
#else
-
HANDLE client_daemon;
-
DWORD dwThreadIdArray;
-
client_daemon =
CreateThread(
-
NULL,
// default security attributes
-
0,
// use default stack size
-
client_refresher,
// thread function name
-
&client,
// argument to thread function
-
0,
// use default creation flags
-
&dwThreadIdArray);
// returns the thread identifier
-
#endif
-
-
/* start publishing the time */
-
printf(
"%s is ready to begin publishing the time.\n", argv[
0]);
-
printf(
"Press ENTER to publish the current time.\n");
-
printf(
"Press CTRL-D (or any other key) to exit.\n\n");
-
while(
fgetc(stdin) ==
'\n') {
-
/* get the current time */
-
time_t timer;
-
time(&timer);
-
struct
tm* tm_info =
localtime(&timer);
-
char timebuf[
26];
-
strftime(timebuf,
26,
"%Y-%m-%d %H:%M:%S", tm_info);
-
-
/* print a message */
-
char application_message[
256];
-
snprintf(application_message,
sizeof(application_message),
"The time is %s", timebuf);
-
printf(
"%s published : \"%s\"", argv[
0], application_message);
-
-
/* publish the time */
-
mqtt_publish(&client, topic, application_message,
strlen(application_message) +
1, MQTT_PUBLISH_QOS_0);
-
-
/* check for errors */
-
if (client.error != MQTT_OK) {
-
fprintf(stderr,
"error: %s\n",
mqtt_error_str(client.error));
-
exit_example(EXIT_FAILURE, sockfd, &client_daemon);
-
}
-
}
-
-
/* disconnect */
-
printf(
"\n%s disconnecting from %s\n", argv[
0], addr);
-
#if defined(__UNIX__)
-
sleep(
1);
-
#else
-
Sleep(
1000);
-
#endif
-
-
/* exit */
-
exit_example(EXIT_SUCCESS, sockfd, &client_daemon);
-
}
-
-
#if defined(__UNIX__)
-
void exit_example(int status, int sockfd, pthread_t *client_daemon)
-
{
-
if (sockfd !=
-1)
close(sockfd);
-
if (client_daemon !=
NULL)
pthread_cancel(*client_daemon);
-
exit(status);
-
}
-
#else
-
void exit_example(int status, int sockfd, HANDLE client_daemon)
-
{
-
if (sockfd !=
-1)
close(sockfd);
-
if (client_daemon !=
NULL)
CloseHandle(client_daemon);
-
exit(status);
-
}
-
#endif
-
-
-
-
void publish_callback(void** unused, struct mqtt_response_publish *published)
-
{
-
/* not used in this example */
-
}
-
-
#if defined(__UNIX__)
-
void* client_refresher(void* client)
-
#else
-
DWORD WINAPI
client_refresher
(LPVOID client)
-
#endif
-
{
-
while(
1)
-
{
-
mqtt_sync((
struct mqtt_client*) client);
-
#if defined(__UNIX__)
-
usleep(
100000U);
-
#else
-
Sleep(
100);
-
#endif
-
}
-
return
NULL;
-
}
点击visual studio编译后运行，这个程序会去连接test.mosquitto.org的1883接口，然后订阅datetime主题，当用户在命令行点击换行后将发布消息到datetime主题，消息内容为当前时间。
在另外一个mqtt客户端订阅这个主题后会收到发布的消息：
转载：https://blog.csdn.net/oushaojun2/article/details/128318713
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