We are using IAR Embedded workbench to create Libraries.
When we compile project using these libraries, we are facing to an issue :
if application layer implements a function with same name as a function defined in a Library, 'duplicate definition' error is notified during application compilation.
In order to avoid this error type, I just want to know if there is a way to hide internal APIs and also internal symbols (global variables...) of compiled Library?
Thank you in advance
For internal functions and variables which are used only in single compilation unit, you can give them internal linkage with static keyword:
/*library.c*/
static int internalLinkageVar;
static void internalLinkageFunc(void);
This will of course not work for symbols which must be accessible to multiple .c files in library. For those it is best to use resonably long prefix on symbol name:
int MyLibrary_Private_Var2;
void MyLibrary_Private_Func(void);
Related
I am building a C ++ library for Windows, Linux / Unix based on CMake.
I create a shared library(.dll) on Windows, and I want to use a static library(.a) on Linux / Unix.
On Windows, I know how to do __declspec(dllexport/dllimport) for every function and class I want to export.
Then I saw these articles recently. (https://blog.kitware.com/create-dlls-on-windows-without-declspec-using-new-cmake-export-all-feature/)
I tried to build CMakeLists.txt without __declspec() in the library function as described in the article.
include(GenerateExportHeader)
generate_export_header(mylibrary)
According to the article, in order to export the static member variables in the class, it is necessary to create the export header according to the existing method and to declare the variables as below.
#include <mylibary_export.h>
class MyClass
{
static mylibrary_EXPORT int GlobalCounter;
...
}
The library has been compiled successfully, but attempting to reference this GlobalCount variable in the downstream project results in a LINK error.
Do you have an idea on this issue?
I am developing a static library, which is added to my main project that tests the static library's functions. The static library inside is using some 3rd party components, and this third party components needs to add some additional libraries (e.g.: libz.dylib, SystemConfiguration.Framework). It's fine, but when I try to build my main project that contains my static library, I got bunch of linker errors. I figured out, if I add the same frameworks and libraries to the main projects what I needed to add to my static library, the linker errors disappear and the project is built succesfully. The question is do I really need to add all of those resources to the main Project? I find it crazy that if I give my static library to someone else to use, I need to include a bunch of frameworks and libraries in the documentation that has to be added also in the integrator project? Or am I missing something important?
It's because a static library is not linked, unlike an executable or dynamic library.
A static library is just an archive of object files, and object files contain external references to symbols they use. Those references are not resolved until the executable/dynamic library is linked.
Therefore when you link-in a static library you are responsible for providing any dependant libraries to the linker, which can themselves be either static or dynamic.
I'm trying to build a GUI using Qt 5.3.1 and having that link to a static lib (built with VisualStudio 2010 using /MD and /MDd). When linking in QtCreator IDE, I get 2 unresolved external linker errors generated from these two function calls from within the static lib.
Both of these (unresolved) functions are declared in WinBase.h.
::InitializeSecurityDescriptor
::SetSecurityDescriptorDacl
What is the easiest solution to get QtCreator to compile this lib? Ideally if possible, I'd like to also link whatever dependency in the static lib itself.
As the documentation of both functions specifies, you have to link against advapi32.lib. In general, all functions of the Windows SDK specify in a box at the end of the documentation the header where they are declared, the header that you should actually include and their import library.
As for the other dependencies, AFAIK there's no way to know - static libraries are just collections of object modules, that specify their dependencies only in terms of imported functions.
Is there any way to get the address of the function which is defined in static library (.lib) which is been linked to some application .
Thanks
A static library is nothing but an archive (like a .ZIP file) of object files.
When you link against a static library the linker will check which of these object files are needed and link them to the executable. The result is exactly the same as if you directly compiled the source code of the library in your project.
So the actual question is: Is it possible to find out the address of a non-static function in an executable file?
Some linkers (like GNU) generate a symbol table by default even in a project without debugging information. You could parse the symbol table in this case. However many linkers do not create this symbol table. In this case the information of all function names is lost so you do not have any chance to get information about the address without debugging information.
I am on OS X, and I have a .so file which I want to link to a .o file during execution. For example Foo.so should be linked to Bar.o during while calling ./Bar.o . I am using the Terminal application to run my app and I compiled my project using a Makefile.
On Unix and OS X you can do this with libdl.
The basic idea is that you compile and link an executable. At some possibly different point in time and place, someone who might not be you compiles and links a shared libray. If at runtime the executable can get strings for the the shared library filename and the symbol of a function that you want to load, then you can use libdl to get a void* to that contains the address of a function in the shared lib. The appropriate function pointer type must be known to the executable at compile time because the next step is to cast the void* to whatever type was "secretly prearranged" between the executable and the dynamically loaded lib. After casting you're good to go.
This tutorial shows the traditional approach for dynamically loading functions. Classes requires some indirection via factory functions.
http://www.tldp.org/HOWTO/html_single/C++-dlopen/
The approach above is where to start but it has the drawback that all communication between the executable and lib must be through C style function signatures created with extern "C" before functions (most significantly no templates or overloads). This is just a limitation on the ports of communication between the executable and lib. Both can use C++ internally. If you want to dynamically import overloaded functions here's a way.
Dynamic Loading Without extern "C"
You have to be careful with user defined classes. The binary representation of classes is not standardized in C++. If a custom class passes from executable to lib but the executable and lib have different ideas of which bits mean what, you won't get the behavior you wanted.
Also, if you compiled your shared library on OS X, you have a dylib, not an so. They're slightly different.
What are the differences between .so and .dylib on osx?