gcc: wrong behaviour after new variable was added

I am writing simple programs: server and client. You know, I am just learning all these stuff.

I added new variable (fileUp in server.c) and the client just crashed. I debugged it with gdb. The client can't read anything from the socket. Without that one variable works fine.

I did compile these programs with both gcc and g++ with -Wall. No errors, no warnings.

Programs are as simple as they can be. I don't understand what is wrong.

Any hint'll be appreciated.

server.c

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char **argv) {
  struct sockaddr_in address, client;
  int s = socket(AF_INET, SOCK_STREAM, 0);

  memset(&address, 0, sizeof(address));
  address.sin_family = AF_INET;
  add开发者_C百科ress.sin_addr.s_addr = htonl(INADDR_ANY);
#define PORT 54321
  address.sin_port = htons(PORT);


  if(bind(s, (struct sockaddr *)&address, sizeof(address))<0) {
    perror("nie udał się bind");
    exit(-1);
  }

  if(listen(s, 5)<0) {
    perror("nie udał się listen");
    exit(-1);
  }

  socklen_t client_len;
  int c = accept(s, (struct sockaddr *)&client, &client_len);

  int file = open("../data", O_RDONLY);
  if(file<0) {
    perror("nie udało się otworzyć pliku");
    exit(-1);
  }

#define MAX 1024
  char buf[MAX];
  int n = read(file, buf, MAX);
  int fileUp = n;

  do {
    write(c, buf, MAX);
    buf[n-1] = '\0';
    printf("%d: %s\n", n, buf);
    /*fileUp += n;
      printf("pobrano: %d\n", fileUp);*/
    n = read(file, buf, MAX);
    getchar();
  } while(n != 0);

  close(c);
  close(s);

  return 0;
}

client.c

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char **argv) {
  struct sockaddr_in address;
  int s = socket(PF_INET, SOCK_STREAM, 0);

  memset(&address, 0, sizeof(address));
  address.sin_family = AF_INET;
#define PORT 54321
  address.sin_port = htons(PORT);

  if(inet_pton(AF_INET, argv[1], &address.sin_addr) <=0) {
    perror("podano nieprawidłowy adres");
    exit(-1);
  }

  if(connect(s, (struct sockaddr *)&address, sizeof(address))<0) {
    perror("nie można się połączyć");
    exit(-1);
  }

#define MAX 1024
  char buf[MAX];
  int n = read(s, buf, MAX);
  int fileDown = n;

  do {
    buf[n-1] = '\0';
    printf("%d: %s\n", n, buf);
    n = read(s, buf, MAX);
    fileDown += n;
    printf("pobrano: %d\n", fileDown);
  } while(n != 0);

  close(s);
  return 0;
}

socklen_t client_len; should be socklen_t client_len = sizeof(client);

The stack layout will change when you add your new variable - so the uninitialized value in client_len just happened to work before, it doesn't after - most likely making your accept call fail, and then you're trying to write to an invalid FD.

You should of course also check the return value of accept