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суббота, 17 декабря 2011 г.

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

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