Files C++

Ok, before the exam, I started repeating files, and now I want to post some of mine notes.

Basic steps to use files:

1. Declare an ofstream/ ifstream/ftream var.

2. Open a file with it.

3. Do stuff to the file (there are couple of ways.)

4. Close it.

ifstream              - open the file for input (reading)

ofstream             - open the file for output (writing)

fstream               - open the file for input/output/both

file. open ("test.txt", ios::in | ios::out | ios::app)

I got a bit confused here, why do I need open AND constructor? Wouldn't it be a lot easier to have just open, or just a constructor... Any way, I'll research it a bit later

flag value           means

ios::in                   open file for reading

ios::out                 open file for writing

ios::app                open for writing,add to end of file(append).

ios::binary             binary file

ios::nocreate         do not create the file,open only if it exists

ios::noreplace       open and create a new file if the specified file does not exist

ios::trunc              open a file and empty it.(Boom, all the data is gone,if any)

ios::ate                 goes to end of file instead of the beginning

Returns current position, if in the end, return length of file:

file.tellg ( );                       

 

Move courser:

seekg/seekp (pos, ios)               

pos – number of bites to move

ios – move from, beg, end, cur

value      means...
ios::beg    beginning of the stream buffer
ios::cur     current position in the stream buffer
ios::end    end of the stream buffer

file.read (buffer,size);

buffer – where to put text

size – how much, counting from seekg

size = sizeof("LOOOOL");

file.write ("LOOOOL",size);

This puts text inside a "file" document.I still need some time to figure out the way it adds, it should be based on seekp position, but I'll figure it out, I just need to make a few examples, I'm planning on making some kind of "holiday calendar" using a text file tomorrow.

eof()                     returns true if the end of the file has been reached

Other functions for reading:

1.seekg();           //move the read pointer in bytes

2.tellg();              //returns where the read pointer is in bytes

Other functions for writing:

1.seekp();           //move the write pointer in bytes

2.tellp();              //returns where the write pointer is in bytes