I want to ask, why I cannot transfer file from server to client? When I start to send the file from server, the client side program will have problem. So, I spend some times to check the code, But I still cannot find out the problem Can anyone point out the problem for me? thanks a lot! [client side code] include include include include include include include define SA struct sockaddr define S_PORT 5678 define MAXLEN 1000 define true 1 void errexit(const char *format, ...) { va_list args; va_start(args, format); vfprintf(stderr, format, args); va_end(args); WSACleanup(); exit(1); } int main(int argc, char *argv []) { WSADATA wsadata; SOCKET sockfd; int number,message; char outbuff[MAXLEN],inbuff[MAXLEN]; char PWD_buffer[_MAX_PATH]; struct sockaddr_in servaddr; FILE *fp; int numbytes; char buf[2048]; if (WSAStartup(MAKEWORD(2,2), &wsadata) != 0) errexit("WSAStartup failed\n"); if (argc != 2) errexit("client IPaddress"); if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET ) errexit("socket error: error number %d\n", WSAGetLastError()); memset(&servaddr, 0, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(S_PORT); if ( (servaddr.sin_addr.s_addr = inet_addr(argv[1])) == INADDR_NONE) errexit("inet_addr error: error number %d\n", WSAGetLastError()); if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) == SOCKET_ERROR) errexit("connect error: error number %d\n", WSAGetLastError()); if ( (fp = fopen("C:\\users\\pc\\desktop\\COPY.c", "wb")) == NULL){ perror("fopen"); exit(1); } printf("Still NO PROBLEM!\n"); //Receive file from server while(1){ numbytes = read(sockfd, buf, sizeof(buf)); printf("read %d bytes, ", numbytes); if(numbytes == 0){ printf("\n"); break; } numbytes = fwrite(buf, sizeof(char), numbytes, fp); printf("fwrite %d bytes\n", numbytes); } fclose(fp); close(sockfd); return 0; } server side code include include include include include include include include define SA struct sockaddr define S_PORT 5678 define MAXLEN 1000 void errexit(const char *format, ...) { va_list args; va_start(args, format); vfprintf(stderr, format, args); va_end(args); WSACleanup(); exit(1); } int main(int argc, char *argv []) { WSADATA wsadata; SOCKET listenfd, connfd; int number, message, numbytes; int h, i, j, alen; int nread; struct sockaddr_in servaddr, cliaddr; FILE *in_file, *out_file, *fp; char buf[4096]; if (WSAStartup(MAKEWORD(2,2), &wsadata) != 0) errexit("WSAStartup failed\n"); listenfd = socket(AF_INET, SOCK_STREAM, 0); if (listenfd == INVALID_SOCKET) errexit("cannot create socket: error number %d\n", WSAGetLastError()); memset(&servaddr, 0, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(S_PORT); if (bind(listenfd, (SA *) &servaddr, sizeof(servaddr)) == SOCKET_ERROR) errexit("can't bind to port %d: error number %d\n", S_PORT, WSAGetLastError()); if (listen(listenfd, 5) == SOCKET_ERROR) errexit("can't listen on port %d: error number %d\n", S_PORT, WSAGetLastError()); alen = sizeof(SA); connfd = accept(listenfd, (SA *) &cliaddr, &alen); if (connfd == INVALID_SOCKET) errexit("accept failed: error number %d\n", WSAGetLastError()); printf("accept one client from %s!\n", inet_ntoa(cliaddr.sin_addr)); fp = fopen ("client.c", "rb"); // open file stored in server if (fp == NULL) { printf("\nfile NOT exist"); } //Sending file while(!feof(fp)){ numbytes = fread(buf, sizeof(char), sizeof(buf), fp); printf("fread %d bytes, ", numbytes); numbytes = write(connfd, buf, numbytes); printf("Sending %d bytes\n",numbytes); } fclose (fp); closesocket(listenfd); closesocket(connfd); return 0; }