I am reading at the time the "Effective C++" written by Scott Meyers and came across the term "translation unit".
Could somebody please give me an explanation of:
What exactly it is?
When should I consider using it while programming with C++?
Is it related to C++ only, or it can be used with other programming languages as well?
I might already use it without knowing the term...
From here: (wayback machine link)
According to standard C++ (wayback machine link) : A translation unit is the basic unit of compilation in C++. It consists of the contents of a single source file, plus the contents of any header files directly or indirectly included by it, minus those lines that were ignored using conditional preprocessing statements.
A single translation unit can be compiled into an object file, library, or executable program.
The notion of a translation unit is most often mentioned in the contexts of the One Definition Rule, and templates.
A translation unit is for all intents and purposes a file (.c/.cpp), after it's finished including all of the header files.
A hard question to answer definitively. The C++ standard states:
The text of the program is kept in units called source files in this International Standard. A source file together with all the headers (17.4.1.2) and source files included (16.2) via the preprocessing directive #include, less any source lines skipped by any of the conditional inclusion (16.1) preprocessing directives, is called a translation unit. [Note: a C++ program need not all be translated at the same time. ]
So for most intents and purposes a translation unit is a single C++ source file and the header or other files it includes via the preprocessor #include mechanism.
Regarding your other questions:
- When should I consider using it when programming with C++
You can't not use it - translation units are the basis of a C++ program.
- If it is related only to C++, or it can be used with other programming languages
Other languages have similar concepts, but their semantics will be subtly different. Most other languages don't use a preprocessor, for example.
The book makes it clear enough. When Meyers referes to a "translation Unit", he means a source code file.
A translation unit is code that is passed to the compiler proper. This typically means the output from running the preprocessor on the .c file.
Every cpp/c (implementation) file will be converted into a translation unit (ie.,object file (.obj)) headers in the cpp file will be replaced with the actual text from the header files.
As others have said, a translation unit is basically the contents of a source file after preprocessing. It's the topmost production in the language grammar; you would only need to worry about it if you were writing a C or C++ compiler.
