C file reading stuff

Anima · 14-03-2007 02:56PM #1

Hey,

I'm trying to read info from a wav header. I have to extract the sampling frequency and a few other details. I can do this with a pretty easy method but I'm trying to do it another way.

FILE *p;
	int buffer[6]={0},x;

	//open the file
	p=fopen("sine.wav","rb");
		
	//read the file
	fread(buffer,sizeof(char),4,p);	//read sampling rate

Instead of just reading each piece of data bit by bit, I want to just select which data I want. My lecturer said I could increment the pointer "p" to create a kind of offset and just read which part I want. I can't seem to get it right though. Is it possible to do it this way?

daymobrew · 14-03-2007 03:03PM

Look at fseek.

/* nError will be 0 on success, -1 otherwise. */
nError = fseek( p, nOffsetFromStart, SEEK_SET );

Changing 'p' directly is not right. Either the lecturer is wrong or maybe you misheard/misinterpreted the info.

kenmc · 14-03-2007 03:16PM

Yeah as Damo says don't change 'p' - it is the handle to your file - if you try to close the file handle and it has been moved who knows what the hell will happen!?

So If I fully understand your question:
Rather than read in the first 4 bytes to only use the 4th one, you want to just read in the 4th one alone?
So yeah - the sequence would be something like
fopen()
fseek(offset=4)
fread(1 byte)
whatever else
fclose

Anima · 14-03-2007 05:29PM

Cheers lads.

C file reading stuff

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