LwIP development | socket | DNS domain name resolution

** Reference resources ：**https://blog.csdn.net/Chuangke_Andy/article/details/113116289

** significance ：** Improve each platform lwip TCP/UDP Programming compatibility , Portability

Environmental Science :
1.freertos
2. Turn on LWIP_SOCKET
3. Bgi, HC32F4A0( Compatible )

code

#include "tcp_client_test.h"
#include "lwip/opt.h"
#include <lwip/sockets.h>
#include "lwip/sys.h"
#include "lwip/api.h"
#include "string.h"

#if LWIP_SOCKET 

#define DEST_PORT 6134// Destination address port number  
#define DEST_IP "192.168.2.195"/* Destination address IP, This is set as local */ 
#define MAX_DATA 1024// The maximum amount of data received  

#define LWIP_TCP_DEBUG_ENABLE 1
#if LWIP_TCP_DEBUG_ENABLE
   #define LWIP_TCP_DEBUG printf
#else
  #define LWIP_TCP_DEBUG(...)
#endif

void tcp_client_thread(void)
{
    
	int sockfd,new_fd;/*cocket Handle and handle after receiving connection  */
    struct sockaddr_in dest_addr;/* Destination address information */
    char buf[MAX_DATA];// Store received data  
	
    sockfd=socket(AF_INET,SOCK_STREAM,0);/* establish socket*/
    if(sockfd < 0)
	{
    
		LWIP_TCP_DEBUG("socket failed:%d",errno);
    }

    dest_addr.sin_family=AF_INET;
    dest_addr.sin_port=htons(DEST_PORT);
    dest_addr.sin_addr.s_addr=inet_addr(DEST_IP);
	
    inet_aton(DEST_IP,&dest_addr.sin_addr);/* Convert the dotted decimal system to 32 Bit integer type */
    if(connect(sockfd,(struct sockaddr*)&dest_addr,sizeof(struct sockaddr)) == -1){
    // Connection method , Incoming handle , Destination address and size  
        LWIP_TCP_DEBUG("connect failed:%d",errno);// In case of failure, you can print errno 
    }
	else
	{
    
        LWIP_TCP_DEBUG("connect success");
        recv(sockfd,buf,MAX_DATA,0);// Enter the received data into buf, The parameters are handles , Storage place , Maximum length , Other information （ Set to 0 that will do ）. 
		LWIP_TCP_DEBUG("Received:%s",buf);
    }
    close(sockfd);// close socket 
	
    return;
}
#endif