Compiled languages basics

Question

Hi,

please, could someone explain to me a few basic things about working with languages like C? Especially on Windows?

1. If I want to use some other library, what do I need from the library? Header files .h and ..?

2. What is the difference between .dll and .dll.a.? .dll and .lib? .dll and .exe? What is .def?

3. Does it matter how was the library compiled? I mean, is it possible to use, on Windows, a C++ library compiled by VC from within my C code compiled by MinGW?

4. To use another library, what is preferred way? LoadLibrary() or #include <>?

5. There are some libraries which only provide the source code or .dll - how to use such libraries? Do I have to recompile them every time I rebuild my project?

6. How do I create one big .exe? Is this called "static linking"?

7. How to include some random file into .exe? Say a program icon or start-up song?

8. How do I split my huge .c into smaller ones? Do I need to create for every part a header file which then I include in the part with WinMain() or main()?

9. If there is a library which needs another library, is it possible to combine these two into one file? Say, python26.dll needs msvcr90.dll and Microsoft.VC90.CRT.manifest

10. What happens if I don't free previously allocated memory? Is this going to be cleaned up if the program (process) dies?

Well, so many question... Thanks for every info!

Answer 1

In all seriousness, the place to go to learn how to run your local environment is the documentation for your local environment. After all we on not even know exactly what your environment is, much less have it in front of us.

But here are some answers:

1. You need the headers, and a linkable object of some kind. Or you need the source so that you can build these.

3. It matters that the library is in a format that your linker understands. In c++ and perhaps other languages, it also needs to understand the name mangling that was used.

6. Forcing all the library code to be included in the executable is, indeed, called "static linking".

7. There is at least one StackOverflow question on "resource compilers".

Answer 2

1: If I want to use some other library, what do I need from the library? Header files .h and ..?

... and, usually a *.lib file which you pass as an argument to your linker.

2: What is the difference between .dll and .dll.a.? .dll and .lib? .dll and .exe? What is .def?

This might be useful: Static libraries, dynamic libraries, DLLs, entry points, headers … how to get out of this alive?

3: Does it matter how was the library compiled? I mean, is it possible to use, on Windows, a C++ library compiled by VC from within my C code compiled by MinGW?

Yes, it matters. For interop between compilers, the normal way is to use a C-style (not C++-style) API, with well-defined parameter-passing conventions (e.g. __stdcall), or to use 'COM' interfaces.

4: To use another library, what is preferred way? LoadLibrary() or #include <>?

#include is for the compiler (e.g. so that it can compile calls to the library); and LoadLibrary (or, using a *.lib file) is for the run-time linker/loader (so that it can substitute the actual address of those library methods into your code): i.e. you need both.

5: There are some libraries which only provide the source code or .dll - how to use such libraries? Do I have to recompile them every time I rebuild my project?

If it's only source then you can compile that source (once) into a library, and then (when you build your project) link to that library (without recompiling the library).

6: How do I create one big .exe? Is this called "static linking"?

Yes, compile everything and pass it all to the linker.

7: How to include some random file into .exe? Say a program icon or start-up song?

Define that in a Windows-specific 'resource file', which is compiled by the 'resource compiler'.

8: How do I split my huge .c into smaller ones? Do I need to create for every part a header file which then I include in the part with WinMain() or main()?

Yes.

9: If there is a library which needs another library, is it possible to combine these two into one file? Say, python26.dll needs msvcr90.dll and Microsoft.VC90.CRT.manifest

I don't understand your question/example.

10: What happens if I don't free previously allocated memory? Is this going to be cleaned up if the program (process) dies?

Yes.

Answer 3

If I want to use some other library, what do I need from the library? Header files .h and ..?

You need header .h or .hpp for C,C++ although some languages don't require header files. You'll also need .a, .so, .dll, .lib, .jar etc files. These files contain the machine code that you linker can link into your program. Goes without saying that the format of library is must be understood by you linker.

What is the difference between .dll and .dll.a.? .dll and .lib? .dll and .exe? What is .def?

dll and .a are library files, that contain code components that you can link into your own program. a .exe is your final program into which .a or .dll has already been linked.

Does it matter how was the library compiled? I mean, is it possible to use, on Windows, a C++ library compiled by VC from within my C code compiled by MinGW?

Yes, it is important that the library that you are using is compatible with your platform. Typically Unix libraries will not run on windows and vice versa, if you are using JAVA you are better off since a .jar files will usually work on any platform with JAVA enabled (though versions matter )

To use another library, what is preferred way? LoadLibrary() or #include <>?

include is not a way to use a library its just a preprocessor directive telling you preprocessor to include a external source file in your current source file. This file can be any file not just .h although usually it would be .h or a .hpp You'll be better off my leaving the decision about when to load a library to you runtime environment or your linker, unless you know for sure that loading a library at a particular point of time is going to add some value to your code. The performance cost and exact method of doing this is platform dependent.

There are some libraries which only provide the source code or .dll - how to use such libraries? Do I have to recompile them every time I rebuild my project?

If you have source code you'll need to recompile it every time you make a change to it. however if you have not changed the source of library in anyway there is no need to recompile it. The build tool like Make are intelligent enough to take this decision for you.

How do I create one big .exe? Is this called "static linking"?

Creating a static .exe is dependent on the build tool you are using. with gcc this would usually mean that you have to you -static option gcc -static -o my.exe my.c

How to include some random file into .exe? Say a program icon or start-up song?

Nothing in programming is random. If it were we would be in trouble. Again the way you can play a song or display an icon is dependent on the platform you are using on some platforms it may even be impossible to do so.

How do I split my huge .c into smaller ones? Do I need to create for every part a header file which then I include in the part with WinMain() or main()?

You'll need a header file with all your function prototypes and you can split you program into several .c files that contain one or more functions. You main files will include the header file. All source files need to be compiled individually and then linked into one executable. Typically you'll get a .o for every .c and then you link all the .o together to get a .exe

If there is a library which needs another library, is it possible to combine these two into one file? Say, python26.dll needs msvcr90.dll and Microsoft.VC90.CRT.manifest

Yes one library may require another library however its not advisable to package different libraries together, you may be violating the IPR and also for the fact that each library is usually a well define unit with a specific purpose and combining them into one usually doesn't make much sense.

What happens if I don't free previously allocated memory? Is this going to be cleaned up if the program (process) dies?

Again depends on the platform, usually on most OS the memory will be recovered after the program dies but on certain platforms like an embedded system it may be permanently lost. It always a good idea to clean up the resources your program has used.