Making my own C++ Library

Have you tried the "static library" project template?

A .o file is an object file. It is an intermediate file that the linker uses to build a final executable. You normally don't do anything at all with .o files. If you are building small projects, you may not have any .o files at all.

Could you explain a little bit about what exactly you want to do? Perhaps you really don't need a library after all. I'm not really sure.

Normally, when writing an application, you have a set of source code files. One of those should contain a main() function. If you want to use code defined in a library, you will #include the appropriate header files from the library. The easiest way to do this on MacOS X is with frameworks, which takes care of the details for you. If not using frameworks, you can just tell Xcode which static or dynamic library you want to link with, providing details like the link path and search path. Then Xcode will compile your code into .o files and link them with all the libraries you have specified.

Migs,

I think this is one way to do what you're trying to do. I started with an empty Xcode project and it seemed to work OK for this simple example. In general though, if you don't understand all the various build settings, I think it can get complicated pretty quickly if you try to manually create complex projects starting from an empty project. I'm did this in Xcode 3.1.2.

*_Create an empty Xcode Project_*
Launch Xcode and "File -> New Project..." to create a new "Empty Project". At this point you'll have no source files and no targets in the project.

*_Create a new target for building your library_*
Do "Project -> New Target...". Select "BSD" and then select "Object file". Name the target "MyLibrary" and click "Finish". In the "Groups & Files" pane of your Xcode window you should now have a "MyLibrary" entry under the "Targets" group and under the top project icon you should have a "Products" folder that shows a "MyLibrary.o" item (this will be colored red since it doesn't exist yet).

*_Create the source files for your library_*
Select "File -> New File...", selecte "C and C++" and then "C++ File". Click "Next". Name your file "MyLibrary.cpp" (and check the checkbox to "also create MyLibrary.h"). Make sure the checkbox is checked to add the files to the "MyLibrary" target. Click "Finish"

You could now paste the code from your original post into the .h and .cpp files... Except the code you posted for the .h file was not quite right. You posted:

Miguel Reznicek wrote:
/*
Program name: mylibrary.h
==============================================
Inclusions: */

#include <iostream>
using namespace std;

void testfunction(){ //simple function code:
cout<<"This is a function"<<endl;
}</div>
But your .h file typically should just contain prototypes for your library functions and not executable statements (so the "cout" code shouldn't be there... it goes into your .cpp file). You probably want something like this:

#include <iostream>
using namespace std;
void testfunction();

The code you posted for your .cpp file is ok except that it should include your "MyLibrary.h" (but that include is typically inserted automatically for you when you use Xcode's "New file..." to create the .cpp and .h files. Like this:

#include "MyLibrary.h"
#include <iostream>
using namespace std;
void testfunction(){ //simple function code:
 cout<<"This is a function"<<endl;
}

Once you've save the two files you should be able to build your "MyLibrary" target and the "MyLibrary.o" product should change from red to black indicating your library was created. You won't be able to run anything however because you don't have a "main" function and you're not building a complete application yet.

*_Create a second new target for building your application_*
Do "Project -> New Target...". Select "BSD" and then select "Shell Tool". Name the target "MyApp" and click "Finish". In the "Groups & Files" pane of your Xcode window you should now have a "MyApp" entry under the "Targets" group and under the top project icon you should have a "Products" folder that shows a "MyApp" item (this will be colored red since it doesn't exist yet).

*_Set up the application target so it is dependent on and links with your library_*
Single click the "MyApp" target in the Groups & Files pane to select it and then click the "Info" button in the toolbar.

In the "General" pane of the info window click the "+" button under "Direct Dependencies". Select "MyLibrary" and then click "Add target". Doing this make your "MyApp" target dependent on the "MyLibrary" target... this tells Xcode that if you attempt to build your "MyApp" then Xcode will check to see if the library has changed and rebuild it first if needed.

Now click the "+" button under "Linked Libraries". Select "MyLibrary.o" and click "Add". Doing this causes your app to link with your library's .o (object file) when you build your app.

*_Create a source file for your application_*
Select "File -> New File...", selecte "C and C++" and then "C++ File". Click "Next". Name your file "main.cpp" (at this point you don't need a .h file for "main" so you can uncheck the checkbox). And in this case make sure the checkbox is checked to add the files to the "MyApp" target (not "MyLibrary"). Click "Finish". Open up "main.cpp" and paste in the code for your "main()" function. You main file should include your library's .h file as shown below.

#include <iostream>
#include "MyLibrary.h"
int main (int argc, char * const argv[]) {
 // insert code here...
 std::cout << "Hello, World! ";
 testfunction(); // Here's the call to your library function
 return 0;
}

You can now switch Xcode's "Active Target" to "MyApp" and you should be able to build and run the application. The output should show the "Hello, World!" from the main function as well as the "This is a function" output from the call to your library.

Steve