The <iostream> library automatically defines a few standard objects:

• cout, an object of the ostream class, which displays data to the standard output device.
• cerr, another object of the ostream class that writes unbuffered output to the standard error device.
• clog, like cerr, but uses buffered output.
• cin, an object of the istream class that reads data from the standard input device.

The <fstream> library allows programmers to do file input and output with the ifstream and ofstream classes.

C++ programmers can also do input and output from strings by using the String Stream class.

Some of the behavior of the C++ I/O streams (precision, justification, etc) may be modified by manipulating various io stream format flags.

Here are some examples of what you can do with C++ I/O.

Display all entries for C++ I/O on one page, or view entries individually:

I/O Constructors	constructors
bad	true if an error occurred
clear	clear and set status flags
close	close a stream
eof	true if at the end-of-file
fail	true if an error occurred
fill	manipulate the default fill character
flags	access or manipulate io stream format flags
flush	empty the buffer
gcount	number of characters read during last input
get	read characters
getline	read a line of characters
good	true if no errors have occurred
ignore	read and discard characters
open	open a new stream
peek	check the next input character
precision	manipulate the precision of a stream
put	write characters
putback	return characters to a stream
rdstate	returns the state flags of the stream
read	read data into a buffer
seekg	perform random access on an input stream
seekp	perform random access on output streams
setf	set format flags
sync_with_stdio	synchronize with standard I/O
tellg	read input stream pointers
tellp	read output stream pointers
unsetf	clear io stream format flags
width	access and manipulate the minimum field width
write	write characters