File Handling In C++

File Handling In C++ How To Work With File handling in C++? 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A stream can be represented as a source or destination of characters of indefinite length depending on its usage.In C++ we have a set of file handling methods. These include ifstream, ofstream, and fstream. These classes are derived from fstrembase and from the corresponding iostream class. These classes, designed to manage the disk files, are declared in fstream and therefore we must include fstream and therefore we must include this file in any program that uses files.In C++, files are mainly dealt by using three classes fstream, ifstream, ofstream.ofstream: This Stream class signifies the output file stream and is applied to create files for writing information to filesifstream: This Stream class signifies the input file stream and is applied for reading information from filesfstream: This Stream class can be used for both read and write from/to files.All the above three classes are derived from fstreambase and from the corresponding iostream class a nd they are designed specifically to manage disk files. C++ provides us with the following operations in File Handling:Creating a file: open()Reading data: read()Writing new data: write()Closing a file: close()Moving on with article on File Handling in C++Opening a FileGenerally, the first operation performed on an object of one of these classes is to associate it to a real file. This procedure is known to open a file.We can open a file using any one of the following methods: 1. First is bypassing the file name in constructor at the time of object creation. 2. Second is using the open() function.To open a file useopen() functionSyntaxvoid open(const char* file_name,ios::openmode mode);Here, the first argument of the open function defines the name and format of the file with the address of the file.The second argument represents the mode in which the file has to be opened. The following modes are used as per the requirements.ModesDescriptioninOpens the file to read(default for ifstre am)outOpens the file to write(default for ofstream)binaryOpens the file in binary modeappOpens the file and appends all the outputs at the endateOpens the file and moves the control to the end of the filetruncRemoves the data in the existing filenocreateOpens the file only if it already existsnoreplaceOpens the file only if it does not already existExample fstream new_file; new_file.open(newfile.txt, ios::out); In the above example, new_file is an object of type fstream, as we know fstream is a class so we need to create an object of this class to use its member functions. So we create new_file object and call open() function. Here we use out mode that allows us to open the file to write in it.Default Open Modes :ifstream ios::inofstream ios::outfstream ios::in | ios::outWe can combine the different modes using or symbol | .Exampleofstream new_file;new_file.open(new_file.txt, ios::out | ios::app );Here, input mode and append mode are combined which represents the file is opened for writing and appending the outputs at the end.As soon as the program terminates, the memory is erased and frees up the memory allocated and closes the files which are opened. But it is better to use the close() function to close the opened files after the use of the file.Using a stream insertion operator we can write information to a file and using stream extraction operator we can easily read information from a file.Example of opening/creating a file using the open() function #includeiostream #include fstream using namespace std; int main() { fstream new_file; new_file.open(new_file,ios::out); if(!new_file) { coutFile creation failed; } else { coutNew file created; new_file.close(); // Step 4: Closing file } return 0; } Output:Explanation In the above example we first create an object to class fstream and name it new_file. Then we apply the open() function on our new_file object. We give the name new_file to the new file we wish to create and we set the mode to out which allows us to write in our file. We use a if statement to find if the file already exists or not if it does exist then it will going to print File creation failed or it will gonna create a new file and print New file created.Moving on with article on File Handling in C++Writing to a FileExample: #include iostream #include fstream using namespace std; int main() { fstream new_file; new_file.open(new_file_write.txt,ios::out); if(!new_file) { coutFile creation failed; } else { coutNew file created; new_fileLearning File handling; //Writing to file new_file.close(); } return 0; } Output:ExplanationHere we first create a new file new_file_write using open() function since we wanted to send output to the file so, we use ios::out. As given in the program, information typed inside the quotes after Insertion Pointer got passed to the output file.Moving on with this article on File Handling in C++Reading from a FileExample #include iostream #include fstream using namespace std; int main() { fstream new_file; new_file.open(new_file_write.txt,ios::in); if(!new_file) coutNo such file; } else { char ch; while (!new_file.eof()) { new_file ch; cout ch; } new_file.close(); return 0; } Output:ExplanationIn this example, we read the file that generated id previous example i.e. new_file_write. To read a file we need to use in mode with syntax ios::in. In the above example, we print the content of the file using extraction operator . The output prints without any space because we use only one character at a time, we need to use getline() with a character array to print the whole line as it is.Moving on with this article on File Handling in C++Close a FileIt is simply done with the help of close() function.Syntax: File Pointer.close()Example #include iostream #include fstream using namespace std; int main() { fstream new_file; new_file.open(new_file.txt,ios::out); new_file.close(); return 0; } Output:The file gets closed.Thus we have come to an end of this article on File Handling in C++. If you wish to learn more, check out theJava Trainingby Edureka, a trusted online learning company. Edurekas Java J2EE and SOA training and certification course is designed to train you for both core and advanced Java concepts along with various Java frameworks like Hibernate Spring.Got a question for us? 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