Related functions: send, sendmsg, recv, recvfrom, socket

Header file: #include <sys/>   #include <sys/>

Define function: int sendto(int s, const void * msg, int len, unsigned int flags, const struct sockaddr * to, int tolen);

Function description: sendto() is used to transfer data from the specified socket to the other host. Parameter s is a socket with a built-in connection. If the UDP protocol is used, there is no need to go through the connection operation. Parameter msg points to the data content to be connected, parameter flags is generally set to 0. For detailed description, please refer to send(). Parameter to is used to specify the network address to be transmitted, and structure sockaddr is the result length of sockaddr. Parameter tolen is the result length of sockaddr.

Return value: If successful, return the actual number of characters transmitted, return -1 if failed. The error reason is stored in errno.

Error code:
1. EBADF parameter s illegal socket processing code.
2. There is a pointer in the EFAULT parameter pointing to the unaccessible memory space.
3. WNOTSOCK canshu s is a file descriptor, not a socket.
4. EINTR is interrupted by the signal.
5. EAGAIN This action will block the process, but the soket of parameter s is blocked by tutoring.
6. The buffer memory of the ENOBUFS system is insufficient.
7. The parameters passed by EINVAL to the system call are incorrect.

example
#include <sys/>
#include <sys/>
#include <>
#include <>
#define PORT 2345 /*port used */
main()
{
    int sockfd, len;
    struct sockaddr_in addr;
    char buffer[256];
//Create socket
    if(sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror ("socket");
        exit(1);
    }
//Fill in the sockaddr_in structure
    bzero(&addr, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr = hton1(INADDR_ANY);
    if(bind(sockfd, &addr, sizeof(addr)) < 0)
    {
        perror("connect");
        exit(1);
    }
    while(1)
    {
        bezro(buffer, sizeof(buffer));
        len = recvfrom(socket, buffer, sizeof(buffer), 0, &addr &addr_len);
//Show the network address of the client side
        printf("receive from %s\n ", inet_ntoa(addr.sin_addr));
//Return the string to the client side
       sendto(sockfd, buffer, len, 0, &addr, addr_len);
    }
}