Read a line and go back to start

Hi,

I'm trying to create a 3d model loader, so one part requires me count the number of '/' in a line and store it. After that I need to go back to the start of the line so I can get the data.

Here is what I'm trying to do. It seems to work for about 20-30 lines and then corrupts the file. Can anyone see why this approach might cause an error ? or have a better way of doing what I'm trying to do ?

Code:

                        int numVerts = 0,u = 0;
			char c;

			while((c = infile.get()) != '\n'){
				if(c == '/') ++numVerts;
				++u;
			}numVerts /= 2;

			for(; u >= 0; --u){
				infile.unget();
			}

Thanks!

Anyone ?

Also, I added an assert after the for loop ->

Code:

assert(infile.good());

and it does fail after about 20 lines, I checked the file and it seems to be fine.

Any Ideas ?

You could read an entire line into a char array, then process it from there, instead of using "unget".

So, for example, you could, say...

Code:

int i, len, numVerts = 0;
char buffer[10000];

infile.getline(buffer, 10000, '\n');
len = strlen(buffer);

for(i=0; i<len; i++){
  //do your counting here
}

//all your data in that line is now in "buffer"
//say if you would still like to read the data as a stream, then you could use the class
//strstream

istrstream in(buffer);

//you could read from the stream "in" in the same way as you do from "infile".

Aah, Worked like a charm!

Thank you so much!

But If anyone knows, I would still like to know why my previous code failed ?

Well, first of all, I am always wary of things like "unget" and stuff. I've had some bad experience with those.
And, for your case, I think your second loop iterates one more time than necessary.
Say you have N characters in a line, then at the end of the first loop, u = N.
Now if you loop u from N to 0, you get (N+1) iterations, instead of N.
What you should have done is to change the guard condition of the loop to "u>0".

Ah, you are right about the u > 0 condition, that was a typo. Although even if I switch it to u > 0, the stream still fails. I had never used unget() in c++ before so I thought I would try it since I'm used to the ungetch() in c.