C / C++ / MFC

char id[32];         // "DATASET_1"
int  blocksize;
:
: <- various data for an amount of 'blocksize' bytes
:

char id[32];         // "DATASET_2"
int  blocksize;
:
: <- various data for an amount of 'blocksize' bytes
:

char id[32];         // "DATASET_3"
int  blocksize;
:
: <- various data for an amount of 'blocksize' bytes
:

char id[32];
int  blocksize;
FILE* f;

f = fopen(filename, "rb");

while (!feof(f))
{
	fread(id,sizeof(char),32,f);		// read id
	fread(&blocksize,sizeof(int),1,f);	// read blocksize

	if (strcmp(id,"DATASET_1") == 0)
	{
		fread( /*  appropriate reading here */);
	}
	else if (strcmp(id,"DATASET_2") == 0)
	{
		fread( /*  appropriate reading here */);
	}
	else // DATASET unknown
	{
		// skip unknow block of data
		fseek(f,blocksize,SEEK_CUR);
	}
}//while

fclose(f);

CStdioFile inFile;
					
inFile.Open(strpath , CFile::modeReadWrite | CFile::typeBinary);
char buf[80];

while(inFile.ReadString(buf,5))
{   
CString outdatastring;
for (int i =0 ;i < 5; i++)
{
//Do some modifing
//
}
				
inFile.WriteString(outdatastring);//outstring is modifeid CString
}               
inFile.Close();