Siehe C

server .c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <winsock.h>
#include <io.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#endif

int main(void) {

    #ifdef _WIN32
    SOCKET sock, fd;
    WSADATA wsaData;
    WSAStartup(0x102,&wsaData);
    #else
    int sock, fd;
    #endif
    
    struct sockaddr_in server, client;
    
    memset(&server, 0, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = htonl(INADDR_ANY);
    server.sin_port = htons(8080);
    
    sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    bind(sock, (struct sockaddr*)&server, sizeof( server));
    listen(sock, 5);
    
    unsigned int len;
    fd = accept(sock, (struct sockaddr*)&client, &len); 
    
    char buffer[1024];
    
    if( (len = recv(fd, buffer, 1024, 0)) > 0) {
        printf("%s\n", buffer);
        send(sock, buffer, strlen(buffer), 0);
        memset(buffer, 0, 1024);
    }            
       
    return 0;
    
}

client.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <winsock.h>
#include <io.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#endif

int main(void) {

    #ifdef _WIN32
    SOCKET sock, fd;
    WSADATA wsaData;
    WSAStartup(0x102,&wsaData);
    #else
    int sock, fd;
    #endif
    
    struct sockaddr_in server;
    
    memset(&server, 0, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    server.sin_port = htons(8080);
    
    sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    connect(sock, (struct sockaddr*)&server, sizeof(server));

    char buffer[] = "Hello world";
    send(sock, buffer, sizeof(buffer), 0);
    
    unsigned int len;
    if( (len = recv(sock, buffer, 1024, 0)) > 0) printf("%s\n", buffer);            
       
    return 0;
    
}

Um eine Verbindung zu verarbeiten ein multithreaded_server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <winsock.h>
#include <io.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#endif

#ifdef _WIN32
void process_thread(SOCKET s) {
#else
void process_thread(int s) {
#endif

    char buffer[1024];
    memset(buffer, 0, 1024);
    int len;    
    while( (len = recv(s, buffer, 1024, 0)) > 0 ) printf("%s\n", buffer);

}

int main(void) {

    #ifdef _WIN32
    SOCKET sock, fd;
    WSADATA wsaData;
    WSAStartup(0x102,&wsaData);
    #else
    int sock, fd;
    #endif
    
    struct sockaddr_in server, client;
    
    memset(&server, 0, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = htonl(INADDR_ANY);
    server.sin_port = htons(8080);
    
    sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    bind(sock, (struct sockaddr*)&server, sizeof( server));
    listen(sock, 5);
    
    unsigned int len; 
    
    char buffer[1024];
    
    #ifdef _WIN32
    DWORD thread;
    #else
    pthread_t thread;
    #endif
    
    while(1) {
    
        fd = accept(sock, (struct sockaddr*)&client, &len);
        if(fd<0) continue;
        #ifdef _WIN32
        if(!CreateThread(NULL, 0, process_thread, fd, 0, &thread)) continue;
        #else
        if(!pthread_create( &thread , NULL , process_thread , fd)) continue;
        #endif
    
    }        
       
    return 0;
    
}