sockets - Connecting to a device in LAN over TCP/IP using C -

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i'm trying connect device(allen-bradley plc) residing in lan using c. device i'm trying connect not host application listens application (since have no control on it). once connection established, can send , receive packets requesting data. developed working application in c# (using system.net.sockets) connects , communicates device. however, c code i'm writing seems fail @ part establishes connection. here's source code:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #ifdef windows #include <winsock2.h> #else #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #endif  #include <errno.h>   int main() { char *servip = "192.168.10.31";  in_port_t servport = 503;  int sock = socket(af_inet, sock_stream, ipproto_tcp);  if (sock < 0) {     fprintf(stderr, "socket() failed: %s\n", strerror(errno));     exit(1); }  struct sockaddr_in servaddr; memset(&servaddr, 0, sizeof(servaddr));  servaddr.sin_family = af_inet;  int rtnval = inet_pton(af_inet, servip, &servaddr.sin_addr.s_addr); if (rtnval <= 0) {     printf("failed"); exit(1); }  if (connect(sock, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {     printf("failed connecting"); exit(1); } else {     printf("connected"); }  char x[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; printf("tere"); write(sock, x, sizeof(x));  char buffer[1024]; recv(sock, buffer, 1024, 0); printf("data received: %s", buffer);   }

you forgot set port call connect().

you defined servport variable, not assigning servaddr variable.

so should add:

servaddr.sin_port = htons(servport);

or simply:

servaddr.sin_port = htons(503);

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