The __declspec(dllexport) was added in CL 262797 for #30674 (attn @qmuntal @ianlancetaylor @alexbrainman).

It does seem like we may need to generate separate header declarations for compiling the cgo package itself vs. writing out the header file for C callers.

(CC @golang/windows)

@Marco-LIU which failure are you seeing? While it is true that headers should mark symbols defined by a DLL with __declspec(dllimport), I have used the cgo export header, which uses __declspec(dllexport), without problems in multiple projects, either with mingw and msvc.

Anyway, it is probably a good idea to generate a separate declaration for the cgo export header, as @bcmills mentioned.

@Marco-LIU which failure are you seeing? While it is true that headers should mark symbols defined by a DLL with __declspec(dllimport), I have used the cgo export header, which uses __declspec(dllexport), without problems in multiple projects, either with mingw and msvc.

Anyway, it is probably a good idea to generate a separate declaration for the cgo export header, as @bcmills mentioned.

@qmuntal thanks for your reply.
In most case, it is ok, compiler and linker have no error commited. It just makes a confusion for reading. For the go lib developer, there is a different on function declaration with expectation. This could lead other errors....

If I define a helper function in CGO comments, this function should call a exported interface, I must make a forward declaration for this exported interface. Then the compiler(clang) will commit a ERROR. To fix this, __declspec(dllexport) should be added in forward declaration. It also makes a reading confusion, and makes the code uncompatible for Linux or Mac.

EXAMPLE:
in go, build command: go build -buildmode=c-shared -o libadd.go.dll .
// extern "C" {
// extern int Add(int a, int b); // ERROR(redeclaration of 'Add' cannot add 'dllexport' attribute)
// static int TripleAdd(int a, int b, int c) {
// return Add(Add(a, b), c);
// }
import "C"

//export Add
func Add(a, b int) int {
return a+b
}

in generated c header: libadd.go.h
extern __declspec(dllexport) int Add(int a, int b);