![]() ![]() ![]() Ifstream, like istream, keeps an internal get position with the location of the element to be read in the next input operation. The member function clear() can be used to reset the state flags.Īll i/o streams objects keep internally -at least- one internal position: Note that good and bad are not exact opposites ( good checks more state flags at once). 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. eof() Returns true if a file open for reading has reached the end. 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. 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. In addition to good, which checks whether the stream is ready for input/output operations, other 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. 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. We have created a while loop that reads the file line by line, using getline. This last example reads a text file and prints out its content on the screen. reading a text file #include #include #include using namespace std Therefore, we could also have declared the previous myfile object and conduct the same opening operation in our previous example by writing: 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. 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). If the function is called with any value in that parameter the default mode is overridden, not combined.įile streams opened in binary mode perform input and output operations independently of any format considerations. Myfile.open ( "example.bin", ios::out | ios::app | ios::binary) Įach 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: classįor 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).įor fstream, the default value is only applied if the function is called without specifying any value for the mode parameter. 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: If the file is opened for output operations and it already existed, its previous content is deleted and replaced by the new one.Īll these flags can be combined using the bitwise operator OR ( |). If this flag is not set, the initial position is the beginning of the file.Īll output operations are performed at the end of the file, appending the content to the current content of the file. Set the initial position at the end of the file. ![]() 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 In order to open a file with a stream object we use its member function open: 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. This procedure is known as to 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 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. basic file operations #include #include using namespace std ![]()
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