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How To Make A Text File In Dev C++

C++ provides the following classes to perform output and input of characters to/from files:

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 was myfile) and any input or output operation performed on this stream object will be applied to the physical file associated to it. Oct 13, 2013 I advise strongly against building your project in C:Dev-Cpp. How to use auto tune perfectly. Not only is it just a bad idea to pollute the installation folder, there is a bug in Dev-C that causes projects in C:Dev-Cpp or its sub-folders to sometimes fail to build. Secondly, in general if you have a problem getting a tool to work, it is unwise to be doing something unnecessarily and gratuitously unusual; and I would.

Jan 22, 2014 This c Video tutorial introduces you to file handling and explains how to create and open files. You are gonna learn how to use classes such as fstream, ifstream, ofstream, how to create. Call open method to open a file “tpoint.txt” to perform read operation using object newfile. If file is open then Declare a string “tp”. Read all data of file object newfile using getline method and put it into the string tp. Print the data of string tp. Close the file object newfile using close method.

ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.

Hi guys, i need to extract data in txt file. Im using dev c. For example this type of data X Y 12.3 4.4 23.6 5 78.3 8.2. StreamWriter ^fs = gcnew StreamWriter(gcnew String(filename)); fs-Write((gcnew String('ghgh'))); fs-Close; delete fs; you create a text. Ask the user if he would like to send it. If he says yes, this means that this particular message should be tagged as outbox message otherwise it should be.

These classes are derived directly or indirectly from the classes istream and ostream. We have already used objects whose types were these classes: cin Dev

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 file

The 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 was myfile) 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:

`ios::in`	Open for input operations.
`ios::out`	Open for output operations.
`ios::binary`	Open in binary mode.
`ios::ate`	Set the initial position at the end of the file. If this flag is not set, the initial position is the beginning of the file.
`ios::app`	All output operations are performed at the end of the file, appending the content to the current content of the file.
`ios::trunc`	If the file is opened for output operations and it already existed, its previous content is deleted and replaced by the new one.

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:

class	default mode parameter
`ofstream`	ios::out
`ifstream`	ios::in
`fstream`	ios::in ios::out

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

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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 file

When 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 function close. 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 files

Text file streams are those where the ios::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 flags

The following member functions exist to check for specific states of a stream (all of them return a bool value):

bad(): Returns true if a reading or writing operation fails. For example, in the case that we try to write to a file that is not open for writing or if the device where we try to write has no space left.
fail(): Returns true in the same cases as bad(), but also in the case that a format error happens, like when an alphabetical character is extracted when we are trying to read an integer number.
eof(): Returns true if a file open for reading has reached the end.
good(): It is the most generic state flag: it returns false in the same cases in which calling any of the previous functions would return true. Note that good and bad are not exact opposites (good checks more state flags at once).

The member function clear() can be used to reset the state flags.

get and put stream positioning

All 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 type streampos, 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 );
seekp ( position );

Using this prototype, the stream pointer is changed to the absolute position

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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 );
seekp ( 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:

`ios::beg`	offset counted from the beginning of the stream
`ios::cur`	offset counted from the current position
`ios::end`	offset counted from the end of the stream

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:

Type	Member type	Description
`streampos`	`ios::pos_type`	Defined as `fpos<mbstate_t>`. It can be converted to/from `streamoff` and can be added or subtracted values of these types.
`streamoff`	`ios::off_type`	It is an alias of one of the fundamental integral types (such as `int` or `long long`).

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 files

For 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 Synchronization

When we operate with file streams, these are associated to an internal buffer object of type streambuf. 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

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synchronization and takes place under any of the following circumstances:

When the file is closed: before closing a file, all buffers that have not yet been flushed are synchronized and all pending data is written or read to the physical medium.
When the buffer is full: Buffers have a certain size. When the buffer is full it is automatically synchronized.
Explicitly, with manipulators: When certain manipulators are used on streams, an explicit synchronization takes place. These manipulators are: flush and endl.
Explicitly, with member function sync(): Calling the stream's member function sync() causes an immediate synchronization. This function returns an int value equal to -1 if the stream has no associated buffer or in case of failure. Otherwise (if the stream buffer was successfully synchronized) it returns 0.

Previous:
Preprocessor directives

Index

For the input of specific types of variables in the C programming language, you’ll find that the scanf() function comes in handy. It’s not a general-purpose input function, and it has some limitations, but it’s great for testing code or grabbing values.

In a way, you could argue that scanf() is the input version of the printf() function. For example, it uses the same conversion characters (the % placeholder-things). Because of that, scanf() is quite particular about how text is input. Here’s the format:

Scary, huh? Just ignore it for now. Here’s a less frightening version of the format:

In this version, placeholder is a conversion character, and variable is a type of variable that matches the conversion character. Unless it’s a string (char array), the variable is prefixed by the & operator.

The scanf() function is prototyped in the stdio.h header file, so you must include that file when you use the function.

Here are some scanf() examples:

The preceding statement reads an integer value into the variable highscore. This assumes that highscore is an int variable.

The preceding scanf() statement waits for a floating-point value to be input, which is then stored in the temperature variable.

In the preceding line, scanf() accepts the first character input and stores it in the key variable.

The %s placeholder is used to read in text, but only until the first white space character is encountered. So a space or a tab or the Enter key terminates the string. (That sucks.) Also, firstname is a char array, so it doesn’t need the & operator in the scanf() function.

How to read a string with scanf()

One of the most common ways to put the scanf() function to use is to read in a chunk of text from standard input. To meet that end, the %s conversion character is used — just like in printf(), but with input instead of output.

SCANF() SWALLOWS A STRING

Exercise 1: Type the source code from scanf() Swallows a String into a new project, ex0712, in Code::Blocks. Build and run.

Line 5 declares a char array — a string variable — named firstname. The number in the brackets indicates the size of the array, or the total number of characters that can be stored there. The array isn’t assigned a value, so it’s created empty. Basically, the statement at Line 5 sets aside storage for up to 15 characters.

The scanf() function in Line 8 reads a string from standard input and stores it in the firstname array. The %s conversion character directs scanf() to look for a string as input, just as %s is a placeholder for strings in printf()’s output.

Exercise 2: Modify the source code from scanf() Swallows a String so that a second string is declared for the person’s last name. Prompt the user for their last name as well, and then display both names by using a single printf() function.

The number in the brackets (refer to Line 5) gives the size of the char array, or the length of the string, plus one.
When you create a char array, or string variable, ensure that you create it of a size large enough to hold the text. That size should be the maximum number of characters plus one.
The reason for increasing the char array size by one is that all strings in C end with a specific termination character. It’s the NULL character, which is written as . The compiler automatically adds the to the end of string values you create in your source code, as well as text read by various text-input functions.
You must remember to add room for that character when you set aside storage for string input.

How to read values with scanf()

The scanf() function can do more than read strings. It can read in any value specified by a conversion character.

SCANF() EATS AN INTEGER

In scanf() Eats an Integer, the scanf() function reads in an integer value. The %d conversion character is used, just like printf() — indeed, it’s used in Line 9. That character directs scanf() to look for an int value for variable fav.

Exercise 3: Create a project, ex0714, using the source code shown in scanf() Eats an Integer. Build and run. Test the program by typing various integer values, positive and negative.

Perhaps you’re wondering about the ampersand (&) in the scanf() function. The character is a C operator — specifically, the memory address operator. It’s one of the advanced features in C that’s related to pointers. An ampersand must prefix any variable specified in the scanf() function. The exception is an array, such as the firstname char array in scanf() Eats an Integer.

Traktor pro sound setting. Try running the program again, but specify a decimal value, such as 41.9, or type text instead of a number.

Text Generator

The reason you see incorrect output is that scanf() is very specific. It fetches only the variable type specified by the conversion character. So if you want a floating-point value, you must specify a float variable and use the appropriate conversion character; %f, in that case.

Exercise 4: Modify the source code from scanf() Eats an Integer so that a floating-point number is requested, input, and displayed.

Create A Text

You don’t need to prefix a char array variable with an ampersand in the scanf() function; when using scanf() to read in a string, just specify the string variable name.
The scanf() function stops reading text input at the first white space character, space, tab, or Enter key.