Thread: How do I check for a specific missing structure member?

Personally, I'd make a tag in the record itself which denotes its type. I'd make this the first entry in the record.

1) read the tag,
2) backup just before the tag
3) read the whole record based on the tag

ie:

Code:

fread( &tag, sizeof(int), 1, fp );
fseek( fp, -sizeof(int), SEEK_CUR );
fread( tag == 1 ?
    &rec1, sizeof(rec1) : tag == 2 ?
    &rec2, sizeof(rec2) :
    &rec3, sizeof(rec3) ,
    1, fp );

Additionally, you could stick the three records in a union, and read it that way, then validate your records once you've read them. This would mean that when you write them, in binary, the records would end up taking up the same space on disk. The benifit of this is that it provides for fast seek times / lookups.

Quzah.

Sorry I should have been more specific.

I've already written a complete, working program that uses tags to determine the record type, that can find check digit errors, wrong tag code, non-digits in a number string etc.

What the program should also do is to find if a string is 'missing' and there is no definition of 'missing' to go on.

The input file is opened as a .txt file and is line sequential, the record type in question contains a single character code (tag), a 5 digit code, a 20 character name, a 60 character address and a couple of numbers, all saved as strings in a structure.

I use fgets to read the strings into the structure. I've tried using fread into the structure, but, and this is the problem, if say, the name is completely missing, then fgets( structure.name, in_fp, 20 ); will read 20 characters from the address and so on. I've written a function that takes the size of the input structure and compares it with the correct size, but this doesn't appear to work on the secret test file used by Computeach.

I've scoured my Source material and can't find anything that even gives me a clue.

I don't necessarily want a complete answer but a nudge in the right direction would be much appreciated!

Cheers

Use *scanf to scan the string to find whatever delimits your fields. ie:

tag,number,20char,60char

fscanf( fp, "%[^,],", buffer );

Then check the buffer:

num = stlren( buf )
switch ( num )
{
case 1: it's a tag; break;
case 5: it's your code; break;
case 20: it's your name string; break;
case 60: it's your last field; break;
default: it's unknown; break;
}

Quzah.