File Input/Output in C. A file represents a sequence of bytes on the disk where a group of related data is stored. File is created for permanent storage of data. It is a ready made structure. In C language, we use a structure pointer of file type to declare a file. FILE.fp; C provides a number of functions that helps to perform basic file. C programming provides a set of built-in functions to read the given input and feed it to the program as per requirement. When we say Output, it means to display some data on screen, printer, or in any file. C programming provides a set of built-in functions to output the data on the computer screen as well as to save it in text or binary files. Input and Output operations can also be performed in C using the C Standard Input and Output Library (cstdio, known as stdio.h in the C language). This library uses what are called streams to operate with physical devices such as keyboards, printers, terminals or with any other type of files supported by the system.
C++ provides the following classes to perform output and input of characters to/from files:
JDoodle is a free Online Compiler, Editor, IDE for Java, C, C, PHP, Perl, Python, Ruby and many more. You can run your programs on the fly online and you can save and share them with others. Quick and Easy way to compile and run programs online. To keep data permanently, we need to write it in a file. File is used to store data. In this topic, you will learn about reading data from a file and writing data to the file. Auto tune efx 3 t pain setting. Fstream is another C standard library like iostream and is used to read and write on files. These are the data types used for file handling from the fstream library.
These classes are derived directly or indirectly from the classes istream and ostream . We have already used objects whose types were these classes: cin is an object of class istream and cout is an object of class ostream . Therefore, we have already been using classes that are related to our file streams. And in fact, we can use our file streams the same way we are already used to use cin and cout , with the only difference that we have to associate these streams with physical files. Let's see an example:This code creates a file called example.txt and inserts a sentence into it in the same way we are used to do with cout , but using the file stream myfile instead.But let's go step by step: Open a fileThe first operation generally performed on an object of one of these classes is to associate it to a real file. This procedure is known as to open a file. An open file is represented within a program by a stream (i.e., an object of one of these classes; in the previous example, this wasmyfile ) and any input or output operation performed on this stream object will be applied to the physical file associated to it.In order to open a file with a stream object we use its member function open :open (filename, mode); Where filename is a string representing the name of the file to be opened, and mode is an optional parameter with a combination of the following flags:
All these flags can be combined using the bitwise operator OR ( | ). For example, if we want to open the file example.bin in binary mode to add data we could do it by the following call to member function open :Each of the open member functions of classes ofstream , ifstream and fstream has a default mode that is used if the file is opened without a second argument:
For ifstream and ofstream classes, ios::in and ios::out are automatically and respectively assumed, even if a mode that does not include them is passed as second argument to the open member function (the flags are combined).For fstream , the default value is only applied if the function is called without specifying any value for the mode parameter. If the function is called with any value in that parameter the default mode is overridden, not combined.File streams opened in binary mode perform input and output operations independently of any format considerations. Non-binary files are known as text files, and some translations may occur due to formatting of some special characters (like newline and carriage return characters). Since the first task that is performed on a file stream is generally to open a file, these three classes include a constructor that automatically calls the open member function and has the exact same parameters as this member. Therefore, we could also have declared the previous myfile object and conduct the same opening operation in our previous example by writing:Combining object construction and stream opening in a single statement. Both forms to open a file are valid and equivalent. To check if a file stream was successful opening a file, you can do it by calling to member is_open . This member function returns a bool value of true in the case that indeed the stream object is associated with an open file, or false otherwise:
![]() Closing a fileWhen we are finished with our input and output operations on a file we shall close it so that the operating system is notified and its resources become available again. For that, we call the stream's member functionclose . This member function takes flushes the associated buffers and closes the file:Once this member function is called, the stream object can be re-used to open another file, and the file is available again to be opened by other processes. In case that an object is destroyed while still associated with an open file, the destructor automatically calls the member function close .Text filesText file streams are those where theios::binary flag is not included in their opening mode. These files are designed to store text and thus all values that are input or output from/to them can suffer some formatting transformations, which do not necessarily correspond to their literal binary value.Writing operations on text files are performed in the same way we operated with cout :Reading from a file can also be performed in the same way that we did with cin :This last example reads a text file and prints out its content on the screen. We have created a while loop that reads the file line by line, using getline. The value returned by getline is a reference to the stream object itself, which when evaluated as a boolean expression (as in this while-loop) is true if the stream is ready for more operations, and false if either the end of the file has been reached or if some other error occurred.Checking state flagsThe following member functions exist to check for specific states of a stream (all of them return abool value):
The member function clear() can be used to reset the state flags.get and put stream positioningAll i/o streams objects keep internally -at least- one internal position:ifstream , like istream , keeps an internal get position with the location of the element to be read in the next input operation.ofstream , like ostream , keeps an internal put position with the location where the next element has to be written.Finally, fstream , keeps both, the get and the put position, like iostream .These internal stream positions point to the locations within the stream where the next reading or writing operation is performed. These positions can be observed and modified using the following member functions: tellg() and tellp()These two member functions with no parameters return a value of the member typestreampos , which is a type representing the current get position (in the case of tellg ) or the put position (in the case of tellp ).seekg() and seekp()These functions allow to change the location of the get and put positions. Both functions are overloaded with two different prototypes. The first form is:seekg ( position ); Using this prototype, the stream pointer is changed to the absolute position position (counting from the beginning of the file). The type for this parameter is streampos , which is the same type as returned by functions tellg and tellp .The other form for these functions is: seekg ( offset, direction ); Using this prototype, the get or put position is set to an offset value relative to some specific point determined by the parameter direction . offset is of type streamoff . And direction is of type seekdir , which is an enumerated type that determines the point from where offset is counted from, and that can take any of the following values:
The following example uses the member functions we have just seen to obtain the size of a file: Notice the type we have used for variables begin and end :streampos is a specific type used for buffer and file positioning and is the type returned by file.tellg() . Values of this type can safely be subtracted from other values of the same type, and can also be converted to an integer type large enough to contain the size of the file.These stream positioning functions use two particular types: streampos and streamoff . These types are also defined as member types of the stream class:
Each of the member types above is an alias of its non-member equivalent (they are the exact same type). It does not matter which one is used. The member types are more generic, because they are the same on all stream objects (even on streams using exotic types of characters), but the non-member types are widely used in existing code for historical reasons. Binary filesFor binary files, reading and writing data with the extraction and insertion operators (<< and >> ) and functions like getline is not efficient, since we do not need to format any data and data is likely not formatted in lines.File streams include two member functions specifically designed to read and write binary data sequentially: write and read . The first one (write ) is a member function of ostream (inherited by ofstream ). And read is a member function of istream (inherited by ifstream ). Objects of class fstream have both. Their prototypes are:write ( memory_block, size ); read ( memory_block, size ); Where memory_block is of type char* (pointer to char ), and represents the address of an array of bytes where the read data elements are stored or from where the data elements to be written are taken. The size parameter is an integer value that specifies the number of characters to be read or written from/to the memory block.In this example, the entire file is read and stored in a memory block. Let's examine how this is done: First, the file is open with the ios::ate flag, which means that the get pointer will be positioned at the end of the file. This way, when we call to member tellg() , we will directly obtain the size of the file.Once we have obtained the size of the file, we request the allocation of a memory block large enough to hold the entire file: Right after that, we proceed to set the get position at the beginning of the file (remember that we opened the file with this pointer at the end), then we read the entire file, and finally close it: At this point we could operate with the data obtained from the file. But our program simply announces that the content of the file is in memory and then finishes. Buffers and SynchronizationWhen we operate with file streams, these are associated to an internal buffer object of typestreambuf . This buffer object may represent a memory block that acts as an intermediary between the stream and the physical file. For example, with an ofstream , each time the member function put (which writes a single character) is called, the character may be inserted in this intermediate buffer instead of being written directly to the physical file with which the stream is associated.The operating system may also define other layers of buffering for reading and writing to files. When the buffer is flushed, all the data contained in it is written to the physical medium (if it is an output stream). This process is called synchronization and takes place under any of the following circumstances:
C++ standard library provides large possibilities for input and output. C++ uses an abstraction called
stream for input and output operations. A stream is an entity which is used by program to read or write characters. For example, screen, keyboard or a file are represented as streams in C++ Programming language. You do not need to know about details of the used entity or technical specification to work with it.
The following header files are commonly used for input and output in C++: Rc48 vst free download pc.
iostream
We used the
iostream header in the previous programs. You have to include iostream header to work with different streams:
Now you can use the following streams for input and output.
Standard Output Stream – cout
The Standard Output Stream is used to output data on your screen. The object
cout of ostream class is used for this purpose:
cout object is used together with the insertion operator“<<” . endl is a function that inserts new line character and flushes the stream.
You can use cout object to output any built in data type. There is a possibility to use multiple << operators to output different elements by using only one cout object:
Note: you have to include
string header to be able to output a variable of string type:
Standard Input Stream – cin
The Standard Input Stream usually represents the keyboards device. The
cin object of istream class is used to get input from the keyboard:
The input is done by using extraction operator “>>”. This operator extracts data from stream and puts it into a variable:
This line of code means that value of name variable now is set to a string entered from keyboard.
The extraction operator will “extract” characters from the keyboard until you didn’t press “Enter” key. You can make multiple inputs by using operator>> multiple times as you did it for multiple outputs with operator <<:
Un-buffered standard error stream – cerr
Un-buffered standard error stream is used when you need to show an error message immediately. This stream is attached to the default error device. For your computer the standard error device is your screen too. You can use un-buffered standard error stream accessing cerr object which is an instance of
ostream class. The use of cerr is similar to the use of cout . The difference consists in the fact you use your error stream for output and not standard output stream:
buffered standard error stream – clog
clog object of ostream class represents buffered standard error stream. The difference between buffered and un-buffered error stream consists in the fact that each insertion to clog object causes the output to be held in a buffer until the buffer is filled or flushed. The message will be displayed on your screen too. The use of clog object is the same as use of any other objects of ostream class:
While you are studying C++ language you will notice a quite difference in use of different streams. But it is a good habit to use error streams in the case when you need to show information about any error.
iomanip
The
iostream library provides possibilities for input and output but you can’t specify the format of the data to output/input. For this purpose you can use iomanip library:
iomanip provides the following possibilities for input and output format:
setbaseDev C File Input Output Codeacademy Answers
setbase (int base) – function that sets base for the number’s output. The base can be octal, decimal and hexadecimal:
The output is:
setw
setw (int n) – function used to set the width of the output. The parameter is field’s width:
The output in this case is:
123456789
x
As you can see, even the “x” length is only one, its displayed width is 9 characters.
setfill
setfill (char_type c) – function used to set a fill character. In the previous example :
The width is set to 9, but the length of output string is 1. The other 8 characters that precede “x” are blank characters. You can set new fill character for the stream using
setfill function:
‘0’ is set as fill character:
123456789
00000000x setprecision
setprecision (int n); – sets decimal precision for output of floating points values. Parameter n is the value of decimal precision:
The variable to be shown in output has different length of the decimal part according to the precision that is set:
Dev C File Input Output Stream In Java
0.3
0.333 0.33333 setiosflags
setiosflags (ios_base::fmtflags mask); – the output format of the stream is specified by the format flags. You can set a flag to specify the format of the output by using setiosflags functions. The parameter for this function is of type fmtflags. There is a possibility to set following format flags using format masks:
You can set multiple masks by using | operation:
C++ File Input
The output is:
Hello World!
0xa0 +1e-012 = +0x1.197998p-40 resetiosflagsDev C++ File Input Output Example
resetiosflags (ios_base::fmtflags mask) – resets the flag specified by the mask.
Dev C++ File Input Output
It has the opposite effect in comparison with
setiosflags .
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