CODEWITHSUNDEEP
c++class
GrinNare
GrinNare

Reputation: 3

C++ When does class object file get compiled?

I'm new to C++, and having difficulty understanding the steps of class object files getting created and compiled.

Let's say I create 3 files: 1. class header file 2. class cpp file (member function definitions present) 3. main cpp file

/* When I run the main cpp file which includes the class header file (say as "#include class.h"), when does class cpp file get compiled, object file created, and linked?

The reason why I'm having difficulty is that from the compiler point of view, when it sees the main cpp file, there is only the header definition, no member function definition. However, even in the class header file, there is no class cpp file included. How would compiler know to run the class cpp file when it is not referred to in either class header file and the main cpp file? */

Let me clarify my question. // Maybe I've said things I don't even understand lol.

So, basically I'm trying to run a main function in a say 'main.cpp' file. This 'main.cpp' file includes the 'class.h' header (include "class.h"). How would compiler execute the functions defined in header file when member function is not declared in 'class.h?' All my member function declaration is in 'class.cpp,' which is not included in 'class.h' or 'main.cpp.'

Upvotes: 0

Views: 1986

Answers (2)

molbdnilo
molbdnilo

Reputation: 66371

I suspect you're using an IDE, since you mention running cpp files - compilers don't know how to run anything.

Your IDE manages these dependencies for you.
When you press "Run", the IDE will decide which files in your project need compiling, and when the compilation is done it will link all the object files together.
If compilation and linking succeeded, the IDE then launches the executable program.

If you want a better understanding of the concepts, step away from your IDE and do all your compilation and linking on the command line for a while.
(It's not complicated, only tedious.)

Upvotes: 1

Jean-Baptiste Yunès
Jean-Baptiste Yunès

Reputation: 36401

You need to compile every .cpp file. Headers; .h files, are just for declarations, means that to let the compiler determine if you use the functions correctly. Each .cpp contains code and should be translated to machine code (.o files). After all these compilations, you need to link them to build the executable so that every function used is contained in the same file. The following commands can help you (using g++ compiler):

$ g++ -c myclass.cpp            // produces the myclass.o file
$ g++ -c main.cpp               // produces the main.o file
$ g++ -o myapp main.o myclass.o // produces the myapp executable

This is oversimplified for the sake of understanding.

Upvotes: 1

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