[SOLVED] does fstream read/write move file pointer

does fstream read/write move file pointer

This is kind of a simple question that I hope can be answered easily, do the file stream read and write operations move the pointer along? As an example:

cpos=10000;
for (i=0;i<20;i++) {
   dataFile.seekg(cpos+i,ios::beg);
   dataFile.read(carray[i],1);
}

Is it identical (logically) to:

dataFile.seekg(cpos,ios::beg);    
cpos=10000;
for (i=0;i<20;i++) {
    dataFile.read(carray[i],1);
}

In other words, does carray[] contain the same contents regardless of which method is used (I can't see the first method being efficient so I am hoping that the correct answer is yes). If so, is same behavior exhibited by write operations?

Solution

Yes, that is the way it works. Your examples aren't quite the same, though. Your first example reads from 10000, then 10001, then 10002, etc. The second needs a seek outside the loop to set the initial position. To be 100% equivalent, you need to have your second example look like:

cpos=10000;
dataFile.seekg(cpos,ios::beg);
for (i=0;i<20;i++) {
   dataFile.read(carray[i],1);
}