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I added a preprocessor in visual studio, that is, #define GLFWAPI, and then when I ran my program, I found that the program was able to link to the function GLFWAPI int glfwGetKeyScancode(int key). I learned from the official website that any other functions in the DLL are private functions of the DLL, but I clearly did not define GLFWAPI as __declspec(dllexport), that is, #define GLFWAPI __declspec(dllexport). Why can my program still link the glfwGetKeyScancode function?
By the way, the creator of a dynamic link library will use __declspec(dllexport) to export functions. However, the consumer of that dll should use __declspec(dllimport) instead.
Maybe you are not using DLL?
Thank you for Viorel's reply. I am sure that I am using a DLL. Because when I define GLFWAPI as __declspec(dllimport), the program throws an error saying that it cannot find the DLL.
There are various ways to export functions from a dll and __declspec(dllexport) is only one of them. For example, functions can be exported using module definition files containing the EXPORTS statement. See Exporting from a DLL Using DEF Files
Thank you very much for your reply. I was talking to someone and they mentioned that maybe it was because I was using a combination of dll.lib and dll. In this case, dll.lib stores function pointers to functions in the dll. So even though I don't define __declspec(dllexport) for GLFWAPI, my program can still link to functions in the dll. Of course, if I define GLFWAPI as __declspec(dllimport), then my program will definitely not be able to link to the function in the dll.
When building a dll the linker will create an import library (dll.lib) enabling consumers of the dll to successfully link code that uses exported functions when load-time linking is used (i.e., NOT using LoadLibrary/GetProcAddress). An import library is created for exported functions without regard to the method used to export them such as __declspec(dllexport) versus a module definition file.