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I have a C++ dynamic library which defines global symbols - functions. When I compile the library using gcc those symbols are by default visible. It may leads to symbol collisions when an application links to a few libraries. I can put functions in the namespace and hide private functions using the compilation flag -fvisibility=hidden. Then API functions should contain the following attribute: __attribute__ ((visibility ("default")))

Let's assume that I compile a dynamic library on Windows using Microsoft Visual Studio compiler. Some symbols are not defined with __declspec(dllexport) Does it mean that those symbols will be hidden ?

Irbis
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  • Are you trying to compare GCC and ELF shared objects to MSVC and Windows DLLs? Or just Windows DLLs with different compilers? Or something else? – Useless May 05 '21 at 11:33
  • As specified in the question description: GCC and ELF shared objects vs MSVC and Windows DLLs. – Irbis May 05 '21 at 11:45

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Both POSIX and Windows provide different means to control symbol visibility. Source-code annotations (__attribute__((visibility("default"))) and __declspec(dllexport)) are the most common way to do this. Windows __declspec(dllexport) is indeed absolutely equivalent to POSIX -fvisibility=hidden + __attribute__((visibility("default"))) in this respect.

But both platforms also provide other alternatives to set visibility e.g. export symbol files and version scripts on POSIX and DEF files on Windows. These alternatives are less common (mainly because they are less portable and prevent some important optimizations).

So whether __declspec is "enough" and in what sense entirely depends on your project's buildscripts. If DEF files and linker scripts are not used - all symbols not explicitly marked with __declspec(dllexport) will be hidden.

yugr
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