• C input/output streams are primarily defined by iostream, a header file that is part of the C standard library (the name stands for I nput/ O utput Stream ). In C and its predecessor, the C programming language, there is no special syntax for streaming data input or output.
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• We may be able to help a bit more, if you are able to supply output from this command on all NetBackup 'Server' instances which have paths or control of the tape library in question, i.e. Run this on all masters, medias, SAN media servers, which have access to the tape library.
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C - Input and Output - When we say Input, it means to feed some data into a program. An input can be given in the form of a file or from the command line. C programming provides a set.

In the C++programming language, input/output library refers to a family of class templates and supporting functions in the C++ Standard Library that implement stream-based input/output capabilities.^[1][2] It is an object-oriented alternative to C's FILE-based streams from the C standard library.^[3][4]

History[edit]

Bjarne Stroustrup, the creator of C++, wrote the first version of the stream I/O library in 1984, as a type-safe and extensible alternative to C's I/O library.^[5] The library has undergone a number of enhancements since this early version, including the introduction of manipulators to control formatting, and templatization to allow its use with character types other than char.

Standardization in 1998 saw the library moved into the std namespace, and the main header changed from <iostream.h> to <iostream>. It is this standardized version that is covered in the rest of the article.

Overview[edit]

Most of the classes in the library are actually very generalized class templates. Each template can operate on various character types, and even the operations themselves, such as how two characters are compared for equality, can be customized. However, the majority of code needs to do input and output operations using only one or two character types, thus most of the time the functionality is accessed through several typedefs, which specify names for commonly used combinations of template and character type.

For example, basic_fstream<CharT,Traits> refers to the generic class template that implements input/output operations on file streams. It is usually used as fstream which is an alias for basic_fstream<char,char_traits<char>>, or, in other words, basic_fstream working on characters of type char with the default character operation set.

The classes in the library could be divided into roughly two categories: abstractions and implementations. Classes, that fall into abstractions category, provide an interface which is sufficient for working with any type of a stream. The code using such classes doesn't depend on the exact location the data is read from or is written to. For example, such code could write data to a file, a memory buffer or a web socket without a recompilation. The implementation classes inherit the abstraction classes and provide an implementation for concrete type of data source or sink. The library provides implementations only for file-based streams and memory buffer-based streams.

The classes in the library could also be divided into two groups by whether it implements low-level or high-level operations. The classes that deal with low-level stuff are called stream buffers. They operate on characters without providing any formatting functionality. These classes are very rarely used directly. The high-level classes are called streams and provide various formatting capabilities. They are built on top of stream buffers.

The following table lists and categorizes all classes provided by the input-output library.

Header files[edit]

The classes of the input/output library reside in several headers.

• <ios> contains the definitions of ios_base and basic_ios classes, that manage formatting information and the associated stream-buffer.
• <istream> contains the definition of basic_istream class template, which implements formatted input.
• <ostream> contains the definition of basic_ostream class template, which implements formatted output.
• <iostream> contains the definition of basic_iostream class template, which implements formatted input and output, and includes <ios>, <istream> and <ostream>.
• <fstream> contains the definitions of basic_ifstream, basic_ofstream and basic_fstream class templates which implement formatted input, output and input/output on file streams.
• <sstream> contains the definitions of basic_istringstream, basic_ostringstream and basic_stringstream class templates which implement formatted input, output and input/output on string-based streams.
• <iomanip> contains formatting manipulators.
• <iosfwd> contains forward declarations of all classes in the input/output library.

Stream buffers[edit]

There are twelve stream buffer classes defined in the C++ language as the table.

Support classes[edit]

ios_base and basic_ios are two classes that manage the lower-level bits of a stream. ios_base stores formatting information and the state of the stream. basic_ios manages the associated stream-buffer. basic_ios is commonly known as simply ios or wios, which are two typedefs for basic_ios with a specific character type. basic_ios and ios_base are very rarely used directly by programmers. Usually, their functionality is accessed through other classes such as iostream which inherit them.^[6][7]

Typedefs[edit]

Formatting manipulators[edit]

Input/output streams[edit]

C++input/output streams are primarily defined by iostream, a header file that is part of the C++ standard library (the name stands for Input/Output Stream). In C++ and its predecessor, the C programming language, there is no special syntax for streaming data input or output. Instead, these are combined as a library of functions. Like the cstdio header inherited from C's stdio.h, iostream provides basic input and output services for C++ programs. iostream uses the objectscin, cout, cerr, and clog for sending data to and from the standard streams input, output, error (unbuffered), and log (buffered) respectively. As part of the C++ standard library, these objects are a part of the stdnamespace.^[8]

The cout object is of type ostream, which overloads the left bit-shiftoperator to make it perform an operation completely unrelated to bitwise operations, and notably evaluate to the value of the left argument, allowing multiple operations on the same ostream object, essentially as a different syntax for method cascading, exposing a fluent interface. The cerr and clog objects are also of type ostream, so they overload that operator as well. The cin object is of type istream, which overloads the right bit-shift operator. The directions of the bit-shift operators make it seem as though data is flowing towards the output stream or flowing away from the input stream.

Output formatting[edit]

Methods[edit]

Manipulators[edit]

Manipulators are objects that can modify a stream using the << or >> operators.

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Other manipulators can be found using the header iomanip.

Criticism[edit]

Some environments do not provide a shared implementation of the C++ library. These include embedded systems and Windows systems running programs built with MinGW. Under these systems, the C++ standard library must be statically linked to a program, which increases the size of the program,^[9] or distributed as a shared library alongside the program.Some implementations of the C++ standard library have significant amounts of dead code. For example, GNU libstdc++ automatically constructs a locale when building an ostream even if a program never uses any types (date, time or money) that a locale affects,^[10]and a statically linked 'Hello, World!' program that uses <iostream> of GNU libstdc++ produces an executable an order of magnitude larger than an equivalent program that uses <cstdio>.^[11]

There exist partial implementations of the C++ standard library designed for space-constrained environments; their <iostream> may leave out features that programs in such environments may not need, such as locale support.^[12]

Naming conventions[edit]

Examples[edit]

The canonical 'Hello, World!' program can be expressed as follows:

This program would output 'Hello, world!' followed by a newline and standard output stream buffer flush.

The following example creates a file called 'file.txt' and puts the text 'Hello, world!' followed by a newline into it.

References[edit]

1. ^ISO/IEC 14882:2003 Programming Languages — C++. [lib.string.streams]/1
2. ^Stanley B. Lippman, Josee Lajoie (1999). C++ Primer (third ed.). Massachusetts: Addison-Wesley. pp. 1109–1112. ISBN0-201-82470-1.
3. ^Bjarne Stroustrup (1997). The C++ programming language (third ed.). Addison-Wesley. pp. 637–640. ISBN0-201-88954-4.
4. ^Stanley B. Lippman, Josee Lajoie (1999). C++ Primer (third ed.). Massachusetts: Addison-Wesley. pp. 1063–1067. ISBN0-201-82470-1.
5. ^Bjarne Stroustrup. 'A History of C++: 1979–1991'(PDF).
6. ^Stanley B. Lippman, Josee Lajoie (1999). C++ Primer (third ed.). Massachusetts: Addison-Wesley. pp. 1112–1120. ISBN0-201-82470-1.
7. ^'<ios> Visual Studio 2010'. Microsoft MSDN: Visual Studio 2010. Retrieved 28 September 2011.
8. ^Holzner, Steven (2001). C++ : Black Book. Scottsdale, Ariz.: Coriolis Group. p. 584. ISBN1-57610-777-9. ..endl, which flushes the output buffer and sends a newline to the standard output stream.
9. ^'MinGW.org: Large executables'. Retrieved 22 April 2009.
10. ^GNU libstdc++ source code, bits/ios_base.h
11. ^C++ vs. C - Pin Eight
12. ^'uClibc++ C++ library'. Retrieved 6 January 2012.

External links[edit]

In this guide, we will learn how to perform input/output(I/O) operations on a file using C programming language.

C File I/O – Table of Contents

1. Opening a File
2. Reading a File
3. Writing a File
4. Closing a file
5. Reading and writing strings to a file
6. Reading and writing binary files in C

Before we discuss each operation in detail, lets take a simple C program:

A Simple C Program to open, read and close the file

In the above program, we are opening a file newfile.txt in r mode, reading the content of the file and displaying it on the console. lets understand the each operation in detail:

1. Opening a file

fopen() function is used for opening a file.
Syntax:

pointer_name can be anything of your choice.
file_name is the name of the file, which you want to open. Specify the full path here like “C:myfilesnewfile.txt”.

While opening a file, you need to specify the mode. The mode that we use to read a file is “r” which is “read only mode”.
for example:

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The address of the first character is stored in pointer fp.

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How to check whether the file has opened successfully?
If file does not open successfully then the pointer will be assigned a NULL value, so you can write the logic like this:
This code will check whether the file has opened successfully or not. If the file does not open, this will display an error message to the user.

Various File Opening Modes:

The file is opened using fopen() function, while opening you can use any of the following mode as per the requirement.
Mode “r”: It is a read only mode, which means if the file is opened in r mode, it won’t allow you to write and modify content of it. When fopen() opens a file successfully then it returns the address of first character of the file, otherwise it returns NULL.

Mode “w”: It is a write only mode. The fopen() function creates a new file when the specified file doesn’t exist and if it fails to open file then it returns NULL.

Mode “a”: Using this mode Content can be appended at the end of an existing file. Like Mode “w”, fopen() creates a new file if it file doesn’t exist. On unsuccessful open it returns NULL.
File Pointer points to: last character of the file.

Mode “r+”: This mode is same as mode “r”; however you can perform various operations on the file opened in this mode. You are allowed to read, write and modify the content of file opened in “r+” mode.
File Pointer points to: First character of the file.

Mode “w+”: Same as mode “w” apart from operations, which can be performed; the file can be read, write and modified in this mode.
Mode “a+”: Same as mode “a”; you can read and append the data in the file, however content modification is not allowed in this mode.

2. Reading a File

To read the file, we must open it first using any of the mode, for example if you only want to read the file then open it in “r” mode. Based on the mode selected during file opening, we are allowed to perform certain operations on the file.

C Program to read a file

fgetc( ): This function reads the character from current pointer’s position and upon successful read moves the pointer to next character in the file. Once the pointers reaches to the end of the file, this function returns EOF (End of File). We have used EOF in our program to determine the end of the file.

3. Writing to a file

To write the file, we must open the file in a mode that supports writing. For example, if you open a file in “r” mode, you won’t be able to write the file as “r” is read only mode that only allows reading.

Example: C Program to write the file

This program asks the user to enter a character and writes that character at the end of the file. If the file doesn’t exist then this program will create a file with the specified name and writes the input character into the file.

4. Closing a file

The fclose( ) function is used for closing an opened file. As an argument you must provide a pointer to the file that you want to close.

An example to show Open, read, write and close operation in C

How to read/ write (I/O) Strings in Files – fgets & fputs

Here we will discuss how to read and write strings into a file.

s: Array of characters to store strings.
rec_len: Length of the input record.
fpr: Pointer to the input file.
Lets take an example:

Example to read the strings from a file in C programming

In the above example we have used fgets function like this:

Here str represents the string (array of char) in which you are storing the string after reading it from file.
10 is the length of the string that needs to be read every time.
fpr is pointer to file, which is going to be read.

Why I used if(fgets(str, 10, fpr)NULL as a logic to determine end of the file?
In the above examples, we have used chEOF to get to know the end of the file. Here we have used this logic because fgets returns NULL when there is no more records are available to be read.

C Program – Writing string to a file

char *s – Array of char.
FILE *fpw – Pointer (of FILE type) to the file, which is going to be written.

fputs takes two arguments –

str – str represents the array, in which string is stored.
fpw – FILE pointer to the output file, in which record needs to be written.

Point to note about fputs:
fputs by default doesn’t add new line after writing each record, in order to do that manually – you can have the following statement after each write to the file.

C FILE I/O for Binary files

So far, we have learned file operations on text files, what if the files are binary (such as .exe file). The above programs will not work for binary files, however there is a minor change in handling Binary files. The main difference is the file name & modes. Lets understand this with the help of an example. Lets say I have two binary files bin1.exe & bin2.exe – I want to copy content of bin1.exe to bin2.exe:

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Example: Reading and Writing Binary Files in C

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