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POSegmentation Fault in Socket Programming
 

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  1. POSegmentation Fault in Socket Programming
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    <p>I am trying to write a simple server-client communication program on C. But I keep getting the error on the server side as soon as a client tries to connect to the server :</p> <p>Segmentation Fault</p> <p>The Server side code is : </p> <pre><code>#include&lt;stdio.h&gt; #include&lt;stdlib.h&gt; #include&lt;string.h&gt; #include&lt;sys/socket.h&gt; #include&lt;sys/types.h&gt; #include&lt;netinet/in.h&gt; void error(char *); int main(int argc, char *argv[]) { int sockfd, newsockfd, n, serv_size, cli_size, port_no, bindfd, readfd, writefd, listenfd; char sbuffer[256]; char *p; p = &amp;sbuffer[0]; struct sockaddr_in serv_addr, cli_addr; if (argc &lt; 2) error("No port no. Specified!\n"); //creating sever side socket sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd == -1) error("Server side listening Socket could not be created!\n"); bzero((char *)&amp;serv_addr, sizeof(serv_addr)); port_no = atoi(argv[1]); serv_addr.sin_family = AF_INET; serv_addr.sin_port = htons(port_no); serv_addr.sin_addr.s_addr = INADDR_ANY; //binding socket bindfd = bind(sockfd, (struct sockaddr *)&amp;serv_addr, sizeof(serv_addr)); if (bindfd == -1) error("Failed to bind server side socket!\n"); //listening for incoming connections listenfd = listen(sockfd, 5); if (listenfd == -1) error("Failed to lisen to incoming connections!\n"); serv_size = sizeof(serv_addr); cli_size = sizeof(cli_addr); newsockfd = accept(sockfd, (struct sockaddr *)&amp;cli_addr, &amp;serv_size); if (newsockfd == -1) error("Failed to accept connections from client!\n"); printf("Server received connections from %s \n", (char *)inet_ntoa(cli_addr.sin_addr)); while(1) { bzero(p, sizeof(sbuffer)); readfd = read(newsockfd, p, sizeof(sbuffer)); if (readfd == -1) error("Sorry. Unable to read message from client!\n"); printf("Message Received: "); puts(sbuffer); bzero(p, sizeof(sbuffer)); printf("\nEnter Your Message for client: "); gets(sbuffer); writefd = write(newsockfd, p, sizeof(sbuffer)); if (writefd == -1) error("Sorry. Message Could not be sent to client.\n"); printf("Congratulations! Message has been sent to client.\n"); } return 0; } void error(char *msg) { perror(msg); exit(1); } </code></pre> <p>The Client side code is : </p> <pre><code>#include&lt;stdio.h&gt; #include&lt;stdlib.h&gt; #include&lt;string.h&gt; #include&lt;sys/socket.h&gt; #include&lt;sys/types.h&gt; #include&lt;netinet/in.h&gt; #include&lt;netdb.h&gt; void error(char *); int main(int argc, char *argv[]) { int sockfd, newsockfd, port_no, n, connectfd, readfd, writefd; char cbuffer[256]; char *ptr = &amp;cbuffer[0]; struct sockaddr_in serv_addr; struct hostent *he; if (argc != 3) error("Incomplete arguments!\n"); port_no = atoi(argv[2]); he = gethostbyname(argv[1]); if (he == NULL) error("No Such Host!\n"); sockfd = socket(AF_INET, SOCK_STREAM, 0); if(sockfd == -1) error("Sorry. Socket could not be created!\n"); bzero((char *)&amp;serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_port = htons(port_no); serv_addr.sin_addr = *((struct in_addr *)he-&gt;h_addr); connectfd = connect(sockfd, (struct sockaddr *)&amp;serv_addr, sizeof(serv_addr)); if (connectfd == -1) error("Sorry. Could not connect to server.\n"); while(1) { bzero(ptr, sizeof(cbuffer)); printf("\nEnter message for Server: \n"); gets(cbuffer); writefd = write(sockfd, ptr, sizeof(cbuffer)); if (writefd == -1) error("Sorry. Could not send message to Server."); printf("Congratulations! Server Successfully Received your message.\n"); bzero(ptr, sizeof(cbuffer)); readfd = read(sockfd, ptr, sizeof(cbuffer)); if (readfd == -1) error("Sorry. Message from server could not be read.\n"); printf("Message Received: "); puts(cbuffer); } return 0; } void error(char *msg) { perror(msg); exit(1); } </code></pre> <p>This is my compile time warning while compiling serv.c: </p> <pre><code>cc -o s serv.c serv.c: In function ‘main’: serv.c:47:52: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] </code></pre> <p>P.S. : I was using Ubuntu 12.04 where I actually wrote these programs and successfully executed the programs. But i recently migrated to Linux Mint 13 Cinnamon. I recompiled the programs. Probably they successfully executed on Mint too. But now it seems to have caught this bug somehow. </p>
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    1. USIndradhanush Gupta
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    1. COPlease try to not waste others time. At moment code is not indented properly and makes reading it difficult. Also in my experience, indenting code properly is good engineering practice anyway and doing it itself may expose problem you are looking to solve. For own help, print out also errno value after read() and such calls. There are values like EAGAIN which are not errors actually. And after that as someone already hinted below, get debugger and find out where it crashed and why.
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      1. POSegmentation Fault in Socket Programming
      1. USTõnu Samuel
    2. COhttp://www.cs.cmu.edu/~gilpin/tutorial/
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      1. POSegmentation Fault in Socket Programming
      1. USJeyaram
    3. COTry to use new approach with getaddrinfo() instead filling serv_addr struct manually. One more advantage is that getaddrinfo() is supporting IPv6.
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      1. POSegmentation Fault in Socket Programming
      1. UScodewarrior
 

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