Question

I had been reading a few articles on 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.

Answer 1

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.