Continuing on binary input and output in c++


In contrast, the output file we are opening for writing ios:: If it does not, it will be created. If this output file does already exist, its previous contents will be thrown away and will be lost. There are other modes you can use when opening a file, such as append ios:: Reading from or writing to a file: Once a file has been successfully opened, you can read from it in the same way as you would read with cin or write to it in the same way as you write using cout.

Continuing our example from above, suppose the input file consists of lines with a username and an integer test score , e. We might use the files we opened above by copying each username and score from the input file to the output file. In the process, we'll increase each score by 10 points for the output file:.

In the while loop, we keep on reading username and score until we hit the end of the file. This is tested by calling the member function eof. The bad thing about using eof is that if the file is not in the right format e. For this error, eof will not return true it's not at the end of the file Errors like that will at least mess up how the rest of the file is read.

In some cases, they will cause an infinite loop. Random access file is associated with a file pointer, which can be moved directly to any location in the file. Random access is crucial in certain applications such as databases and indexes. You can position the input pointer via seekg and output pointer via seekp. Each of them has two versions: The string streams is based on ostringstream subclass of ostream , istringstream subclass of istream and bi-directional stringstream subclass of iostream.

IO operations are defined for each of the type. If IO operations are not defined for a particular type, compiler will generate an error. The same set of operations can be applied to different types of IO devices. Construct a stream object. Connect Associate the stream object to an actual IO device e. Some functions convert the data between the external format and internal format formatted IO ; while other does not unformatted or binary IO. Disconnect Dissociate the stream to the actual IO device e.

Free the stream object. Take note that istream and ostream are unidirectional streams; whereas iostream is bidirectional.

The unformatted output functions e. It uses the terminating null character to decide the end of the char array. In unformatting input, such as get , getlin , read , it reads the characters as they are, without conversion.

It uses whitespace as delimiter and adds a terminating null character to the C-string. Flushing the Input Buffer - ignore You can use the ignore to discard characters in the input buffer: The last input operation failed to read the expected characters or output operation failed to write the expected characters, e.

Absence of above error with value of 0. However, it is more convenience to use these public member functions of ios class: By default, the values are displayed with a field-width just enough to hold the text, without additional leading or trailing spaces.

You need to provide spaces between the values, if desired. For integers, all digits will be displayed, by default. This default precision of 6 digits include all digits before and after the decimal point, but exclude the leading zeros. Scientific notation E-notation will be used if the exponent is 6 or more or -5 or less. By default, opening an output file creates a new file if the filename does not exist; or truncates it clear its content and starts writing as an empty file.

The available file mode flags are:. You can set multiple flags via bit-or operator, e. For output, the default is ios:: For input, the default is ios:: We need to use read and write member functions for binary file file mode of ios:: Random access file is associated with a file pointer, which can be moved directly to any location in the file.

Random access is crucial in certain applications such as databases and indexes. You can position the input pointer via seekg and output pointer via seekp. Each of them has two versions: The string streams is based on ostringstream subclass of ostream , istringstream subclass of istream and bi-directional stringstream subclass of iostream. IO operations are defined for each of the type. If IO operations are not defined for a particular type, compiler will generate an error.

The same set of operations can be applied to different types of IO devices. Construct a stream object. Connect Associate the stream object to an actual IO device e.

Some functions convert the data between the external format and internal format formatted IO ; while other does not unformatted or binary IO. Disconnect Dissociate the stream to the actual IO device e. Free the stream object. Take note that istream and ostream are unidirectional streams; whereas iostream is bidirectional. The unformatted output functions e. It uses the terminating null character to decide the end of the char array. In unformatting input, such as get , getlin , read , it reads the characters as they are, without conversion.

It uses whitespace as delimiter and adds a terminating null character to the C-string. Flushing the Input Buffer - ignore You can use the ignore to discard characters in the input buffer: The last input operation failed to read the expected characters or output operation failed to write the expected characters, e.

Absence of above error with value of 0.