Explicitly exporting shared library functions in Linux

Question

Is there a Linux equivalent of __declspec(dllexport) notation for explicitly exporting a function from a shared library? For some reason with the toolchain I'm using, functions that aren't class members don't appear in the resulting shared library file.

Elegist

Answer 1

__attribute__((visibility("default")))

And there is no equivalent of __declspec(dllimport) to my knowledge.

#if defined(_MSC_VER)
    //  Microsoft 
    #define EXPORT __declspec(dllexport)
    #define IMPORT __declspec(dllimport)
#elif defined(__GNUC__)
    //  GCC
    #define EXPORT __attribute__((visibility("default")))
    #define IMPORT
#else
    //  do nothing and hope for the best?
    #define EXPORT
    #define IMPORT
    #pragma warning Unknown dynamic link import/export semantics.
#endif

Typical usage is to define a symbol like MY_LIB_PUBLIC conditionally define it as either EXPORT or IMPORT, based on if the library is currently being compiled or not:

#if MY_LIB_COMPILING
#   define MY_LIB_PUBLIC EXPORT
#else
#   define MY_LIB_PUBLIC IMPORT
#endif

To use this, you mark your functions and classes like this:

MY_LIB_PUBLIC void foo();

class MY_LIB_PUBLIC some_type
{
    // ...
};

Deathwatch

A note about where to place the macro would be nice for future readers. – Bellini

@Bellini Place the macro anywhere before you annotate EXPORT/IMPORT on anything. Most projects will have a specific place in some header where all of their global macros are defined. – Galvanize

@DanBechard I guess this was related to the position of the macro when using it on a function or class. There are some examples in the GCC Wiki post; rule of thumb: Use it before the return type of a function, and before a class name, e.g. EXPORT void FunctionName() and class EXPORT ClassName. – Ouidaouija