1. when need to keep permanently
File Input/Output
when need to keep permanently

2. Streams C++ uses streams for input and output
stream - is a sequence of data to be read (input stream) or a sequence of data generated by the program to be output (output stream)
by default only standard streams are declared: cin (console input) cout (console output)
files are used to store information permanently
to do file input/output <fstream> needs to be included
as well as using std::ifstream; and using std::ofstream;
an input or output stream needs to be declared:
ifstream fin; // input stream
ofstream fout; // output stream
before C++ program can read from or write to a file stream, the stream needs to be connected to a file. This is referred to as opening the file:
fin.open(”myfile.dat”); // opening file
string declaration and file opening in single statement
ifstream fin(”myfile.dat”);

3. Streams (Cont.) a string variable can be used as file name
c_str() function has to be applied to the string:
string filename=”myfile.dat”;
fin.open(filename.c_str());
after stream variable has been connected to a file, extraction and insertion operators can be used with a stream:
fin >> var1 >> var2 >> var3;
after the file is opened all the operations on the file is done through associated stream
reading from a file
while(fin >> myvar){ … } // any file
while(getline(fin, myvar)){ … } // text file
iterates until file ends or reading error
closing stream:
fin.close(); // closing file
good style: closing all opened file streams before program ends

4. I/O Error Checking
function fail() returns true if previous stream operation failed
useful to check if file is opened successfully before performing operations on file
useful function exit() - exists program immediately.
to use exit, include <cstdlib>
exit() accepts one integer as argument:
convention: 0 - normal program termination; nonzero - abnormal
example
fin.open(”myfile.dat”); // opening file
if (fin.fail()){
cout << ”Cannot open file myfile.dat”;
exit(1); }

5. Streams as Parameters streams can be passed as parameters
streams must be passed by reference
void myfunc(ifstream &myinfile);

6. File I/O Review what is stream?
what is the difference between input stream and output stream?
what streams do not need definitions?
how can you declare a stream?
what do the following functions do?
open() close()
c_str() eof() fail() exit()
how does one read from a file until its end?
can a stream be passed as a parameter?