Modes of Opening Files

When you open a file (for writing or reading), there are 6 modes that you can use to specify how you want the file to be opened. The modes are :
ios::app
ios::ate
ios::binary
ios::in
ios::out
ios::trunc

Including ios::app causes all the output (or whatever you write) to be appended to the end of the file. This mode can be used only for files opened for output.
ios::in  specifies that the file is capable of input only. ios::out specifies that the file is capable of output.
ios::binary causes the file to be opened in binary mode (I'll deal with binary later on).
ios::trunc causes contents of pre-existing file by same name to be destroyed.

So far we've seen the file opening as follows :

ofstream out;
out.open("test");        // This means test is opened in normal mode.
By default this is the same as  out.open("test", ios::out);         // opened specifically for output

We can combine two modes as follows :
out.open("test", ios::out | ios::binary );

What is Binary?

Reading and writing formatted text is easy. But sometimes you may need to store unformatted data (i.e. in binary or raw form) and not as text. In the next section I'll deal with such functions. When you perform binary operations on a file, you should open it in binary mode. If a file is opened in text mode (or normal mode) and you make use of these functions (that are intended for binary mode), the functions will work. But some character translations will occur. 
Basically there are two types of files that C++ recognizes : binary and text files. Binary files can contain any data representation format. Text files contain only alphanumeric data as represented by the compiler's character set (for example ASCII). By default, all files are opened in text mode unless you specify ios::binary.

Next section we shall take a look at : Put ( ) and Get ( ) functions

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