14.13. I/O Feature Summary

Review

More Portable Data Types

`fmtflags`	Formatting flags: An unsigned 32-bit integer; each bit represents a flag that controls one aspect of the stream's behavior
`openmode`	Represents the bit-vector values that specify file opening modes
`streampos`	The position in a file. Represents the current read/write (get/put) position within a stream
`streamsize`	The size of a file or a number of bytes. A signed integer
`streamoff`	The offset within a file. Use by the "seek" functions

Portable data types used with strings. Unlike the data types whose names end with _t, and that are implemented as symbolic constants, the data types listed here are implemented with templates.

Bit-Masks / Formatting Flags

File Open Modes
`ios::in`	Open for input
`ios::out`	Open for output
`ios::app`	Append data to the end of the output file (repositioning commands are ignored, forcing output at the end)
`ios::ate`	Go to the end of the file when opened (allows repositioning in the file)
`ios::trunc`	Discard contents of existing file
`ios::binary`	Open in binary mode (defaults to text mode)
Formatting Flags
`ios::dec`	read/write integers as decimal (base-10) values
`ios::hex`	read/write integers as hexadecimal (base-16) values
`ios::oct`	read/write integers as octal (base-8) values
`ios::fixed`	force printing of floating point numbers in fixed point notation
`ios::scientific`	force printing of floating point numbers in scientific notation
`ios::left`	align on the left side, pad on the right
`ios::right`	align on the right side, pad on the left
Positioning In A File
`ios::beg`	Change file pointer to the beginning of the file
`ios::end`	Change file pointer to the end of the file
`ios::cur`	Change file pointer relative to the current position

Useful file I/O flags. See Open a file and fmtflags for additional formatting flags.

Manipulators

<iostream> Manipulators
Manipulator	Description	Example
`endl`	Insert an end of line, `\n`, and flush the output buffer (the last character is a lower-case 'L')	endl.cpp
`ends`	Insert a null character, `'\0'`, into the output stream
`dec`	Display output in decimal	base.cpp
`hex`	Display output in hexadecimal
`oct`	Display output in octal
`right`	Right-align, pad on the left (used with setw, see below). Used to format columns in a table - columns of numbers generally look best right justified. Output is right-justified by default; use "right" to reset justification if changed by "left"	align.cpp fill.cpp
`left`	Left-align, pad on the right (used with setw, see below). Used to format columns in a table - columns of strings generally look best left justified.	align.cpp fill.cpp
`fixed`	Display numbers in a fixed decimal point notation (no scientific notation)	notation.cpp
`scientific`	Display numbers in scientific notation	notation.cpp
<iomanip> Manipulators
`setw(int width)`	Sets the output field width; if the output is shorter than the field with, the unused space is padded; the default pad character is a space but can be changed with "setfill." Used to format columns in a table.	align.cpp
`setfill(char fill)`	Sets the padding or fill character when the output field is wider the printed data. The default fill character is a space or blank. Used with `setw`.	fill.cpp
`setprecision(int precision)`	Sets the number of digits displayed after the decimal point (technically, the radix point)	mortgage.cpp
`setbase(int base)`	Sets the base of numeric output to decimal, hexadecimal, or octal
`setiosflags(fmtflags flags)`	Sets the calling stream object's formatting flags to the argument value
`resetiosflags(fmtflags flags)`	Sets to 0 all of the flags in the argument value
`bool is_open()`	True if the file is open; false otherwise. Can be used with `ifstream`, `ofstream`, and `fstream` objects.

Useful Manipulators. See Format flag manipulators and <iomanip> for additional stream manipulators.

Constructors And Open Functions

Constructor	Description	Example
ifstream() ifstream(file_name, ios::open mode = ios::in) open(file_name, openmode mode = ios::in)	Creates a stream object that is not attached to a file. Creates a stream object and opens the named file. Opens a file with an existing `ifstream` object.	wc HTMLfix wc
ofstream() ofstream(file_name, openmode mode = ios::out) open(file_name, openmode mode = ios::out)	Creates a stream object that is not attached to a file. Creates a stream object and opens the named file. Opens a file with an existing `ofstream` object.	HTMLfix
fstream() fstream(file_name, openmode mode = ios::in \| ios::out) open(file_name, openmode mode = ios::in \| ios::out)	Creates a stream object that is not attached to a file. Creates a stream object and opens the named file. Opens a file with an existing `fstream` object.	rolodex(2)

File stream constructors. The "f" in each name indicates a file stream class. The "i" indicates an input stream, while the "o" indicates an output stream. file_name may be a C-string or an instance of the string class.

Member Functions

Function	Description	Example
`ignore(n = 1, delim = '\n')`	Removes and discards `n` characters from the input stream, or stops after the `delim` character is removed or the end-of-file is reached, whichever comes first. For example: `ignore()`, `ignore(10)`, or `ignore(10, ':')`	temp.cpp
`istream& read(char* s, streamsize n)`	Reads `n` bytes from the stream and saves them in the character buffer (array) `s`.	mycopy.cpp
`istream& seekg(streampos pos)` `istream& seekg(streamoff off, [beg, cur, end])`	Moves the "get" position pointer to the absolute position `pos`. Moves the "get" position pointer to the specified offset: beginning, current, or end (see Figure 2).	rolodex(2)
`streampos tellg()`	Returns the current position of the "get" position pointer.
`streamsize gcount()`	Returns the number of byte input by the last read operation.	mycopy.cpp

istream and ifstream member functions. See ifstream for more functions and details.

Function	Description	Example
`char fill(char pad)` `char fill();`	Without an argument, returns the current fill character. With an argument, sets the padding or fill character when the output field is wider the printed data. The default fill character is a space or blank. Used with `setw`. Has the same effect as the `setfill` manipulator.	fill2.cpp
`precision(int digits)`	When either the `fixed` or the `scientific` formatting flags are set or are "on," the `precision` function sets the number of places following the decimal or radix point. See the example program for more details.	precision.cpp
`ostream& write(char* s, streamsize n)`	Writes `n` bytes to the stream from the character buffer (array) `s`.	mycopy.cpp rolodex(2)
`ostream& seekp(streampos pos)` `ostream& seekg(streamoff off, [beg, cur, end])`	Moves the "put" position pointer to the absolute position `pos`. Moves the "put" position pointer to the specified offset: beginning, current, or end (see Figure 2).	rolodex(2)
`streampos tellp()`	Returns the current position of the "put" position pointer.	rolodex(2)
`ostream& flush()`	Forces the system to write data stored in the stream buffer.	rolodex(2)

ostream and ofstream member functions.

Flag Functions

Function	Description	Example
`setf(flags)`	Sets those flags specified in flags while not changing the remaining flags.	flags.cpp mortgage.cpp
`unsetf(flags)`	Clears those flags specified in flags while not changing the remaining flags.
`flags()`	Gets the current formatting flags.
`flags(flags)`	Sets those flags specified in flags while clearing the remaining flags.

Formatting flag functions.

Function	Description	Example
`bool good()`	Returns true if there are not error flags set; returns false otherwise.	mycopy.cpp
`bool bad()`	Return true if the `badbit` is set.
`bool fail()`	Return true if the `failbit` is set.
`bool eof()`	Return true if the `eofbit` is set.
`rdstat()`	Read state: returns a 4-bit vector containing the values of `goodbit`, `badbit`, `failbit`, and `eofbit`.

File state flag functions.