Basics of a C++ Development/execution environments
Assume source code, a program, has been created.
Preprocessor
The preprocessor program processes preprocessor code. It executes
automatically before the compiler stage. It obeys special commands
called preprocessor directives which indicate that certain manipulations
are to be performed on the program before compilation.
These manipulations typically consist of including other files or telling
the compiler to define some code as it may be repeated and it
shouldn't be stored twice.
For example, typically in files defining classes, the #ifndef
tells the compiler to do what follows if the definition is not already
in the symbol table under the given name. The symbol table is a huge data
structure of every identifier in your program and everything the compiler
needs to know about it. The #define says to define it
associated with the given name as follows in the code.
The #endif terminates the #ifndef directive.
This is explained further via the Rational example in the
Rational class header file.
Compiler
The compiler creates object code and stores it on disk. It is a special
type of translator; it translates source code into machine language code
(same as object code). In the beginning you will care mostly about
the compiler errors, the error messages. Eventually compiler errors become
no big deal, but in the beginning when you don't know all of the language,
they can be confusing. If you leave off a semicolon, misspell, forget a
parenthesis, mess up your curly braces, etc., you get a compiler error.
Often the compiler doesn't determine an error until it goes beyond what
is really wrong, so always look at the line after the error. C++ error
messages are not as clear as Java error messages. And you can get many,
many of them for doing one simple thing wrong. Always correct the first
error and recompile before trying to figure out the rest. Often they
aren't true errors, are propogated because of the first error,
and will disappear.
Linker
The linker links the object code with the libraries, creates an executable
file and stores it on disk. When you refer to something in a library,
the compiler leaves a hole for the address where it can be found and the
linker must resolve the addressing. In other words, it must find it to create a
complete executable file.
When you get a linking error, it can't find something. Usually it's a typo.
Function signatures (the header) etc., must be identical to what is in
the .cpp file. Also, your #includes may be wrong.
Loader
The loader puts the program in memory so the CPU can take each instruction
and execute it. It will likely store new data values as the program executes.
What is the difference between a compiler and interpreter?
While a compiler translates high level language into machine code to later
be loaded and executed, an interpreter takes the high level code and
immediately carries out the instruction. There are also hybrid systems
where high level code is translated into intermediate code
(e.g., Java byte code) and then the instruction is performed by an interpreter.