Programming

#include <stdio.h>
#include <io.h>

#include <stdio.h>

//#define LINUX /* define this if you are on linux   */
//#define WIN32 /* define this if you are on windows */

#ifdef WIN32
#       include "io.h"
#       include "winsock2.h"      /* WSAGetLastError, WSAStartUp  */
#       define snprintf _snprintf
#endif

#ifdef LINUX
#       include <netdb.h>         /* gethostbyname  */
#       include <netinet/in.h>    /* htons          */
#       include <sys/socket.h>
#endif

static void sendmail_write(
                const int  sock,
                const char *str,
                const char *arg
            ) {
    char buf[4096];

    if (arg != NULL)
        snprintf(buf, sizeof(buf), str, arg);        
    else
        snprintf(buf, sizeof(buf), str);
    
    send(sock, buf, strlen(buf), 0);
}

static int sendmail(
                const char *from,
                const char *to,
                const char *subject,
                const char *body,
                const char *hostname,
                const int   port
            ) {
    struct hostent *host;   
    struct sockaddr_in saddr_in;
    int sock = 0;

#ifdef WIN32
   WSADATA wsaData;
   if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
      return -1;
   }
#endif

    sock = socket(AF_INET, SOCK_STREAM, 0);
   host = gethostbyname(hostname);
   
   saddr_in.sin_family      = AF_INET;
   saddr_in.sin_port        = htons((u_short)port);
   saddr_in.sin_addr.s_addr = 0;

   memcpy((char*)&(saddr_in.sin_addr), host->h_addr, host->h_length);

   if (connect(sock, (struct sockaddr*)&saddr_in, sizeof(saddr_in)) == -1) {
      return -2;
   }
    
    sendmail_write(sock, "HELO %s\n",       from);    // greeting
    sendmail_write(sock, "MAIL FROM: %s\n", from);    // from
    sendmail_write(sock, "RCPT TO: %s\n",   to);      // to
    sendmail_write(sock, "DATA\n",          NULL);    // begin data

    // next comes mail headers
    sendmail_write(sock, "From: %s\n",      from);
    sendmail_write(sock, "To: %s\n",        to);
    sendmail_write(sock, "Subject: %s\n",   subject);

    sendmail_write(sock, "\n",              NULL);

    sendmail_write(sock, "%s\n",            body);    // data

    sendmail_write(sock, ".\n",             NULL);    // end data
    sendmail_write(sock, "QUIT\n",          NULL);    // terminate

    close(sock);

    return 0;
}


int main(int argc, char *argv[]) {
    
    int ret = sendmail(
        "from@from-host.org",   /* from     */
        "to@to-host.org",       /* to       */
        "Subject",              /* subject  */
        "body",                 /* body     */
        "hostname",             /* hostname */
        25                      /* port     */
    );

    if (ret != 0)
        fprintf(stderr, "Failed to send mail (code: %i).\n", ret);
    else
        fprintf(stdout, "Mail successfully sent.\n");

    return ret;
}