c++ #include (what functions are in what) - c++

I am a fairly seasoned Java programmer, so i understand what including does, and why to do it, BUT, I am using java for a example, When i need a method i can go to the structure and open the jars and see what is there, but i have been watching some tut's and they say you are going to need to include this .h file because it has this function etc, So the question: I typed #include<.h> and got a list of all the .h files, but NOWHERE do i see what is in those files, so if i need to use a function that gets to the system properties(Just a example), how do you know what to include, I am really not liking C right now for this only reason.

functions do not exist in a header file (.h). They exist in .lib, .so, .dll etc files depending on whether they are static or dynamic and depending on the operating system. The header file just declares/prototypes the function. Typically the documentation of a function tells you which header it's declared in.
Header files are text files. You can open them in any text editor to see them, to see what functions they declare.
Typically, if the documentation doesn't tell me the header (rare), I go to the headers directory and either do a grep (on Linux/Unixes) or a findstr on windows to figure out where the function I want is declared.
Another thing to know is that including the right header file will help in compilation of your program but may not ensure that your program will link to build the final binary. For that you link with the right lib file. Again the documentation of the function will tell which is the right lib to link with. In the microsoft world, some header files may have a pragma lib entry which ensures that including the header automatically links in the right lib file.
A lot of the documentation is also available online - msdn, cppreference etc.

Related

how to include certain header files by default so that i don't have to type them in every programs

how to include certain header files by default so that i don't have to type them in every programs:
In dev c++ and code::blocks
Make a global header file that in turn includes whatever files you need in every project, and then you only have to include that single file.
However I would recommend against it, unless all your different project are very similar. Different projects have different needs and also need different header files.
You could issue a compiler directive in your project file or make script to do "per project" includes, but in general I would avoid that.
Source code should be as clear as possible to any reader just by its content. Whenever I have source code that dramatically changes its semantics, eg. by headers that are unknown to me, this can be quite confusing.
On top of that, if you "inject" those headers for certain compilation units that don't need them, that will negatively impact compile time.
As a substitution, what about introducing a common.h/hpp header that includes those certain header files? You can then include your common header in all files that need them and change this common set of headers for all depending files at once. It also opens the door to use precompiled header files, which may be worth a look for you.
From GCC documentation (AFAIK GCC is default compiler used by the development environment you are citing)
-include file
Process file as if #include "file" appeared as the first line of the primary source file. However, the first directory searched for
file is the preprocessor's working directory instead of the directory
containing the main source file. If not found there, it is searched
for in the remainder of the #include "..." search chain as normal.
If multiple -include options are given, the files are included in the order they appear on the command line.
-imacros file
Exactly like -include, except that any output produced by scanning file is thrown away. Macros it defines remain defined. This allows you
to acquire all the macros from a header without also processing its
declarations.
All files specified by -imacros are processed before all files specified by -include.
But it is usually a bad idea to use these.
Dev c++ works with MingW compiler, which is gcc compiler for Windows. Gcc supports precompiled headers, so you can try that. Precompiled headers are header files that you want compiled and added to every object file in a project. Try searching for that in Google for some information.
Code::blocks supports them too, when used with gcc, even better, so there it may even be easier.
If your editor of choice supports macros, make one that adds your preferred set of include files. Once made, all you have to do is invoke your macro to save yourself the repetitive typing and you're golden.
Hope this helps.

Difference between C++ files

I just started a graphical C++ course and I have problem getting an overview how it is.
we got some starting code, two files; one of type "C++ Source" and another of "C/C++ Header".
its supposed to be a graphical program which fills the screen with color.
also, we are using some custom libraries such as SDL and GLM, in the same folder as those two files there is a folder named gml and loads of subfolders, which I wont get into.
I have downloaded mingw, cmake and Visual Studio 11 beta for c++.
I've tried making a normal Win32 program and also a forms-application for the graphical part, but its always something wrong when compiling.
My question: how are you supposed to handle C++ files? I just got used to java and there its so easy to just open the .java file and paste into your IDE, dealing with C++ makes me really confused.
Hmm... Where to begin...
Somethings that happen behind the scenes in other languages are much more visible in C++. The process of obtaining a binary (say, an executable) from C++ involves first compiling the source code (There are sub-steps of this but the compiler handles them) to obtain object files, then the object files are linked by the linker to generate a binary.
In theory, you could simply #include all the cpp files in a project, and compile them all together and "link" (although there's nothing to link) but that would take a very long time, and more importantly, in complex projects that could deplete the memory available to your compiler.
So, we split our projects into compilation units, and by convention a .cpp file represents a single compilation unit. A compilation unit is the part of your project that gets compiled to generate one object file. Even though compilation units are compiled separately, some code has to be common among them, so that the piece of code in each of them can use the functionalities implemented by the others. .h files conventionally serve this purpose. Things are basically declared (sort of announced) in them, so that each compilation unit knows what to expect when it's a part of a linking process to generate a binary.
There's also the issue with libraries. You can find mainly two kinds of things in libraries;
Already implemented functionality, shipped to you in the form of binary files including CPU instructions that can almost be run (but they've to be inserted in the right place). This form is accompanied by .h files to let your .cpp files know what to expect in the library.
The second type is functionality implemented directly in the .h
files. Yes, this is possible under special cases. There are cases,
where the implementation has to (a weak has to) accompany the
declaration (inlined functions, templated types etc.).
The first type comes in two flavors: A "static library" (.lib in windows, .a in linux), that enters your executable and becomes a part of it during linking, and a "dynamic library", that is exposed to your binary (so it knows about it) but that doesn't become a part of it. So, your executable will be looking for that dynamic library (.dll files in windows and .so files in linux f.x.) while it's run.
So, in order for your .cpp files to be able to receive services from libraries, they have to #include their .h files, to know about what there is in them. Later on, during linking, you have to show the linker where (what path in the file system) to find the binary components of those libraries. Finally, if the library is dynamic, the .dll's (or .so's etc.) must be accessible during run time (keep them in the same folder for instance).
While compiling your compilation units you have to tell the compiler where to find the .h files. Otherwise, all it will see will be #include <something.h> and it won't know where to find that file. with gcc, you tell the compiler with the -I option. Note that, you just tell the folder. Also of importance is that if the include directive looks like #include<somefolder/somefile.h> you shouldn't include somefolder in the path. So the invocation looks like:
g++ mycompilationunit.cpp -IPATH/TO/THE/INCLUDED/FILES -IPATH/TO/OTHER/INCLUDED/FILES -c
The -c option tells the compiler that it shouldn't attempt to make an executable just from this compilation unit, so it creates a .o file, to be linked with others later. Since we don't tell it the output file name, it spits out mycompilationunit.o.
Now we want to generate our binary (you probably want an executable, but you could also want to create a library of yours). So we have to tell the linker everything that goes into the binary. All the object files and all the static and dynamic libraries. So, we say: (Note g++ here also acts as the linker)
g++ objectfile1.o objectfile2.o objectfile3.o -LPATH/TO/LIBRARY/BINARIES -llibrary1 -llibrary2 -o myexecutable
Here, -L option is self explanatory in the example. -l option tells which binaries to look for. The linker will accept both static and dynamic libraries if it finds them on the path, and if it finds both, it'll choose one. Note that what goes after -l is not the full binary name. For instance in linux library names take the form liblibrary.so.0 but they're referred to as -llibrary in the linker command. finally -o tells the compiler what name to give to your executable. You need some other options to f.x. create a dynamic library, but you probably don't need to know about them now.
What is the difference between a .cpp file and a .h file?
Look at this answer. Also a quick google search explains a bit too.
Pretty much .h (header) files are declerations and .cpp (source) files are definitions. It is possible to combine both files into one .cpp file but as projects get bigger and bigger its becomes annoying and almost unreasonable.
Hope that helps.
In C++ there is a notion of a function declaration (the function signature) and a function definition (the actual code).
A header file (*.h) contains the declarations of functions and classes. A source file (*.cpp, *.c++, *.C) contains the definitions.
A header file can be included in a source file using #include directive.
When you define a class in C++, you typically only include the declarations of the member functions (methods in Java lingo), and you put the class definition into a header file. The member function definitions containing the body of each function are typically put outside the class definition and into the source file.
Generally the best thing to do here is to get a book on C++ or C, and to look at some sample code.
Header files (.h) are supposed to contain definitions of classes, methods, and variables. Source file (.cpp) will contain the code. So in your .cpp file you need to include the header file as #include "header-file-name.h".
Then use g++ to compile the .cpp file. Make sure that the path to .h file is correct.
If you are using CodeBlocks or Visual Studio, then just compiling the project and running will do everything for you. You can also add .h or .cpp file from there. You need not worry about anything.
Hope this helps.

Compiling a program with multiple files

I just started learning C++ with Dev C++ as my IDE. One of the tutorials I'm using has a page in it about compiling a program made up of multiple files. It's simple stuff at this point, I have one file with a function in it, and the other file has all the other required code to call the function and output the results. The problem is that the tutorial doesn't tell me how to join these files so I can compile the program and have it work. There's seems to be multiple ways of doing this and I'd like them all but I'm mainly look for the simplest one right now.
I should also mention that I'm new at this so please try and keep your explanations simple and understandable.
In general, you would add both .cpp files to your project under the same target. It IDE will automatically add both files to the build and link them together.
That said, Dev-C++ is very, very old and unmaintained. It has not seen updates in several years. I strongly urge you to use a different IDE. There are many to choose from, including a fork of Dev-C++ called wxDev-C++. I'd actually recommend Code::Blocks or Visual Studio Express, which are both much more modern and have better support for debugging and many other features.
I am not sure of Dev-C++, but the concepts remain the same. So, here is how you can try to get both the files to work together
Each C++ file is a compilation unit - meaning, the compiler will convert one .cpp / .cxx file to one .obj / .o file (on Windows and Linux (or any Unix)) respectively
The obj files, called the object files contain the machine code (am skipping few internal details here) for the classes and functions present in that particular file
If you want to access the functions present in a different compilation unit, you need to link those two object files
Linking is a term that is used to, well, link two object files
There is a separate process (other than the compiler) which does the linking of the object files
So,in your case, you need to use the dev-c++ compiler and create separate object files
Then using the linker you link both the object files to create the final executable
If there are functions that exist in the .cpp files that you want to reference, you use the header files. The header files contain the function/class declarations. The .cpp files will have the implementations. So, in one of your .cpp file, (say) A.cpp, you include the header B.hpp and use the functions in the B.hpp file. The inclusion of headers will tell the compiler that the function declarations exist elsewhere and that the linker will take care of stringing all these references together to create the final executable.
Hope this helps, else, please don't hesitate to mention the files you are using and I can suggest how to link both the .cpp files together.
You must include the other files by using the #include preprocessor directive
in the top of the file where you have the main() function
For example:
#include "filename.h"
...
/* rest of code containing main function goes here */
...
#include "path/filename.c"
main
{
...
...
...
}

could not understand including the header file

#include "Ser.h"
#include ".\ser.h"
Is this .\ser.h is an executable of Ser.cpp...When right clicked on it and when pressed "open the document .\ser.h" its going to the Ser.h file...
Why does they again include the executable file(./ser.h) as header file.... isnt the header file(Ser.h) enough to get all the delarations needed to be defined in.
.\ser.h is not an executable file, it's simply another header file.
In systems where file names are case-irrelevant (and this seems likely here since it's using the Windows path separator \), it may well be just including the same file twice.
If include guards are used correctly, that won't matter. If case is relevant, they're most likely two different files.
I say "may" since the order of searches for header files, and even the mapping of the header-names to headers or files, is implementation defined and xyz.h and ./xyz.h may be found in different places because of this.
There is no way of telling for sure without knowing what your include path is. This is likely just including the same header file twice on a case insensitive platform such as Windows. Which is probably a mistake but a harmless one because of include guards (those #ifdef at the beginning and end of the file).
It seems as if you are having trouble understanding the purpose of header files. There is no such thing as the header file. A header file is just the place where functions and classes are declared but usually not defined. So if ser.cpp uses some function that is defined in common_functions.cpp, you should include the apropriate header - it will usually be called common_functions.h.
Be aware that, as for almost anything in the C or C++ world, there are plenty of exceptions, but the above holds true most of the time.
The ./ser.h is not an executable file. Please keep in mind, file extensions ending in .h are generally header files.
If your platform is windows you will find executable files taking the file extension .exe.
One Ser.h file is enough to receive all the declarations, so you do not need two of the same header files.

LNK4221 and LNK4006 Warnings

I am making a static library of my own. I have taken my code which works and now put it into a static library for another program to use. In my library I am using another static library which I don't want the people who will be using my API to know. Since, I want to hide that information from them I can't tell them to install the other static library.
Anyway, I used the command line Lib.exe to extract and create a smaller lib file of just the obj's I used. However, I get a bunch of LNK4006 :second definition ignored linker warnings for each obj I use followed by LNK4221 no public symbols found;archive member will be inaccessible.
I am doing this work in vs2008 and I am not sure what I am doing wrong.
I am using the #pragma comment line in my .cpp file
I have also modified the librarian to add my smaller .lib along with its location.
my code simply makes calls to a couple functions which it should be able to get from those Obj file in the smaller lib.
All my functions are implemented in .cpp file and my header just have the includes of the third party header files and come standard c++ header files. nothing fancy. I have actually no function definitions in there atm. I was going to put the API definition in there and implement that in the .cpp for this static lib that i was going to make. However, I just wanted to build my code before I added more to it.
I did read http://support.microsoft.com/default.aspx?scid=kb;EN-US;815773 but it did not provide a solution.
Even if you extract all objects from the other library and put them in your own library, your users will still be able to see what's in your library and thus see all the object names. In many cases the names of the objects will reveal what's actually the other library you are using.
Instead of distributing your library as a static library, consider distributing it as a DLL. In the DLL you can easily hide all the underlying things and only make public what you want to make public.