if vs else if. Seems like a huge difference

[mityay]

I'm writing a client-server application. Attached is its simplified version which narrows down my issue. The idea is, that server sends the sturcture of 3 ints. Client receives the structure and based on the values, performs certain actions. This is performed in a loop. Here's a fragment from test_client.c:

numRead = fread(&array, sizeof(struct three_ints), 1, sock_fp);
if (numRead <=0)
	printf("numRead is now &#37;d\n", numRead);
sleep(2);

if (array.one == 0 && array.two == 0 && array.three == 0)
{
printf("Read zeros. Their current values are %d, %d, %d\n", array.one, array.two, array.three);
printf("About to read integers and char. Their current values are %d, %d, %c\n", other_array.intOne, other_array.intTwo, other_array.charOne);

fread(&other_array, sizeof(struct two_ints_char), 1, sock_fp);

printf("Read the integers and char. Their current values are %d, %d, %c\n\n", other_array.intOne, other_array.intTwo, other_array.charOne);
sleep(4);
}

else if ( array.one == -5 && array.two == -5 && array.three == -5 )
{
              printf("I am at -5\n");
}

else if ( array.one == -10 && array.two == -10 && array.three == -10 )   
{
             printf("I am at -10\n");
}

else
{
printf("Read non-zeros. Their current values are %d, %d, %d\n", array.one, array.two, array.three);
printf("About to send some_int to server %d\n", ++some_int);
fwrite(&some_int, sizeof(int), 1, sock_fp);
printf("some_int sent\n\n");
sleep(6);
}

This version works fine. However, once I replace "else if" with just "if" (until recent I believed the outcomes are the same), the following function fails:

numRead = fread(&array, sizeof(struct three_ints), 1, sock_fp);

and numread contains zero value. It took me 2 days to figure it out, but why does it happen and how can "if" statement affect fread function I still have no idea. Can someone explain???

Thanks

[brewbuck]

The ONLY way this could be happening is if this line:

fread(&other_array, sizeof(struct two_ints_char), 1, sock_fp);

Is overwriting the other array.

[Salem]

A couple of things spring to mind.
1. You don't open the streams in binary mode.
2. You're making a lot of assumptions about the size, padding, alignment and endian-ess of those structs as they're represented on the client and the server.

Consider using wireshark / ethereal to trace the messages on the wire.

[mityay]

The ONLY way this could be happening is if this line:

fread(&other_array, sizeof(struct two_ints_char), 1, sock_fp);

Is overwriting the other array.

I didn't change the logic - just replaced "if" with "else if" that's all. And it's not happening anymore. And the line is overwriting the values of other_array structure but I don't think there's anything wrong with that

[brewbuck]

I didn't change the logic - just replaced "if" with "else if" that's all. And it's not happening anymore. And the line is overwriting the values of other_array structure but I don't think there's anything wrong with that

If it's not happening anymore, then I suspect the problem never had anything to do with this piece of code. There's nothing wrong with it.