Sams Teach Yourself C++ in 21 Days

open and close files, you create ifstreamand ofstreamobjects as described in the next

few sections.

Using the ofstream..............................................................................................

The particular objects used to read from or write to files are called ofstreamobjects.

These are derived from the iostreamobjects you’ve been using so far.

To get started with writing to a file, you must first create an ofstreamobject, and then

associate that object with a particular file on your disk. To use ofstreamobjects, you

must be certain to include fstreamin your program.

624 Day 17

Because fstreamincludes iostream, you do not need to include iostream

explicitly.

NOTE

Condition States..............................................................................................

The iostreamobjects maintain flags that report on the state of your input and output.

You can check each of these flags using the Boolean functions eof(),bad(),fail(),

and good(). The function eof()returns trueif the iostreamobject has encountered

EOF, end of file. The function bad()returns trueif you attempt an invalid operation.

The function fail()returns trueanytime bad()is true or an operation fails. Finally, the

function good()returns trueanytime all three of the other functions are false.

Opening Files for Input and Output ..............................................................

To use a file, you must first open it. To open the file myfile.cppwith an ofstream

object, declare an instance of an ofstreamobject and pass in the filename as a

parameter:

ofstream fout(“myfile.cpp”);

This attempts to open the file,myfile.cpp, for output. Opening this file for input works

the same way, except that it uses an ifstreamobject:

ifstream fin(“myfile.cpp”);

Note that foutand finare names you define; here,fouthas been used to reflect its sim-

ilarity to cout, and finhas been used to reflect its similarity to cin. These could also be

given names that reflect what is in the file they are accessing.