Formatted and unformatted input and output and streams

I had been reading a few articles on开发者_如何学编程 some sites about Formatted and Unformatted I/O, however i have my mind more messed up now.

I know this is a very basic question, but i would request anyone can give a link [ to some site or previously answered question on Stackoverflow ] which explains, the idea of streams in C and C++.

Also, i would like to know about Formatted and Unformatted I/O.

The standard doesn't define what these terms mean, it just says which of the functions defined in the standard are formatted IO and which are not. It places some requirements on the implementation of these functions.

Formatted IO is simply the IO done using the << and >> operators. They are meant to be used with text representation of the data, they involve some parsing, analyzing and conversion of the data being read or written. Formatted input skips whitespace:

Each formatted input function begins execution by constructing an object of class sentry with the noskipws (second) argument false.

Unformatted IO reads and writes the data just as a sequence of 'characters' (with possibly applying the codecvt of the imbued locale). It's meant to read and write binary data, or function as a lower-level used by the formatted IO implementation. Unformatted input doesn't skip whitespace:

Each unformatted input function begins execution by constructing an object of class sentry with the default argument noskipws (second) argument true.

And allows you to retrieve the number of characters read by the last input operation using gcount():

Returns: The number of characters extracted by the last unformatted input member function called for the object.

Formatted IO means that your output is determined by a "format string", that means you provide a string with certain placeholders, and you additionally give arguments that should be used to fill these placeholders:

const char *daughter_name = "Lisa";
int daughter_age = 5;
printf("My daughter %s is %d years old\n", daughter_name, daughter_age);

The placeholders in the example are %s, indicating that this shall be substituted using a string, and %d, indicating that this is to be replaced by a signed integer number. There are a lot more options that give you control over how the final string will present itself. It's a convenience for you as the programmer, because it relieves you from the burden of converting the different data types into a string and it additionally relieves you from string appending operations via strcat or anything similar.

Unformatted IO on the other hand means you simply write character or byte sequences to a stream, not using any format string while you are doing so.

Which brings us to your question about streams. The general concept behind "streaming" is that you don't have to load a file or whatever input as a whole all the time. For small data this does work though, but imagine you need to process terabytes of data - no way this will fit into a single byte array without your machine running out of memory. That's why streaming allows you to process data in smaller-sized chunks, one at a time, one after the other, so that at any given time you just have to deal with a fix-sized amount of data. You read the data into a helper variable over and over again and process it, until your underlying stream tells you that you are done and there is no more data left.

The same works on the output side, you write your output step for step, chunk for chunk, rather than writing the whole thing at once.

This concept brings other nice features, too. Because you can nest streams within streams within streams, you can build a whole chain of transformations, where each stream may modify the data until you finally receive the end result, not knowing about the single transformations, because you treat your stream as if there were just one.

This can be very useful, for example C or C++ streams buffer the data that they read natively from e.g. a file to avoid unnecessary calls and to read the data in optimized chunks, so that the overall performance will be much better than if you would read directly from the file system.

Unformatted Input/Output is the most basic form of input/output. Unformatted input/output transfers the internal binary representation of the data directly between memory and the file. Formatted output converts the internal binary representation of the data to ASCII characters which are written to the output file. Formatted input reads characters from the input file and converts them to internal form. Formatted