Fix Visual Studio shared library build

Todo: fluid-shared can't (yet) be built agains the shared fltk lib
  because of some linker errors. Needs investigation.

Note: fluid-shared is basically a test program to demonstrate linking
  against the shared FLTK libs but doesn't work yet using VS (MSVC).
  This is no problem for the functionality.

5 files changed, 17 insertions, 10 deletions

diff --git a/FL/Fl_String.H b/FL/Fl_String.H
index dc0d8307a..f8e273d65 100644
--- a/FL/Fl_String.H
+++ b/FL/Fl_String.H
@@ -126,8 +126,8 @@ public:
 }; // class Fl_String
 
 // ---- Non-member functions
-extern Fl_String operator+(const Fl_String &lhs, const Fl_String &rhs);
-extern Fl_String operator+(const Fl_String &lhs, const char *rhs);
-extern bool operator==(const Fl_String &lhs, const Fl_String &rhs);
+FL_EXPORT Fl_String operator+(const Fl_String& lhs, const Fl_String& rhs);
+FL_EXPORT Fl_String operator+(const Fl_String& lhs, const char* rhs);
+FL_EXPORT bool operator==(const Fl_String & lhs, const Fl_String & rhs);
 
 #endif // _FL_Fl_String_H_
diff --git a/fluid/CMakeLists.txt b/fluid/CMakeLists.txt
index 62eec124d..124547f08 100644
--- a/fluid/CMakeLists.txt
+++ b/fluid/CMakeLists.txt
@@ -166,9 +166,12 @@ if (OPTION_BUILD_SHARED_LIBS)
   list (APPEND FLUID_TARGETS fluid-shared)
   add_executable (fluid-shared fluid.cxx fluid.h)
   if (MSVC)
-    target_link_libraries (fluid-shared fluid-lib fltk_SHARED)
+    # Todo: this should link against fltk_SHARED rather than fltk_images but for an unknown
+    # reason this would issue link errors (about 25 undefined symbols). Needs investigation.
+    # AlbrechtS: Sep. 12, 2023
+    target_link_libraries (fluid-shared PRIVATE fluid-lib fltk_images) # should be: fltk_SHARED)
   else ()
-    target_link_libraries (fluid-shared fluid-lib fltk_images_SHARED)
+    target_link_libraries (fluid-shared PRIVATE fluid-lib fltk_images_SHARED)
   endif (MSVC)
 endif ()
 
diff --git a/png/CMakeLists.txt b/png/CMakeLists.txt
index 065ede0e0..b47323fe4 100644
--- a/png/CMakeLists.txt
+++ b/png/CMakeLists.txt
@@ -85,7 +85,7 @@ if (OPTION_BUILD_SHARED_LIBS)
   FL_ADD_LIBRARY (fltk_png SHARED "${PNG_SRCS}")
 
   if (FLTK_USE_BUILTIN_ZLIB)
-    target_link_libraries (fltk_png_SHARED fltk_z_SHARED)
+    target_link_libraries (fltk_png_SHARED fltk_z)
   else()
     target_link_libraries (fltk_png_SHARED ${FLTK_ZLIB_LIBRARIES})
   endif ()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 9f1a578b8..693726a13 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -831,19 +831,19 @@ if (OPTION_BUILD_SHARED_LIBS AND MSVC)
   target_link_libraries (fltk_SHARED ${OPTIONAL_LIBS})
 
   if (FLTK_USE_BUILTIN_JPEG)
-    target_link_libraries (fltk_SHARED fltk_jpeg_SHARED)
+    target_link_libraries (fltk_SHARED fltk_jpeg)
   else()
     target_link_libraries (fltk_SHARED ${FLTK_JPEG_LIBRARIES})
   endif ()
 
   if (FLTK_USE_BUILTIN_PNG)
-    target_link_libraries (fltk_SHARED fltk_png_SHARED)
+    target_link_libraries (fltk_SHARED fltk_png)
   else()
     target_link_libraries (fltk_SHARED ${FLTK_PNG_LIBRARIES})
   endif ()
 
   if (FLTK_USE_BUILTIN_ZLIB)
-    target_link_libraries (fltk_SHARED fltk_z_SHARED)
+    target_link_libraries (fltk_SHARED fltk_z)
   else()
     target_link_libraries (fltk_SHARED ${FLTK_ZLIB_LIBRARIES})
   endif ()
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 6fb3b5105..1687ebfb8 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -169,7 +169,11 @@ SET (UNITTEST_SRCS
 )
 if (OPENGL_FOUND)
   set (UNITTEST_LIBS fltk_gl fltk ${OPENGL_LIBRARIES})
-  set (UNITTEST_LIBS_SHARED fltk_gl_SHARED fltk_SHARED ${OPENGL_LIBRARIES})
+  if (MSVC)
+    set (UNITTEST_LIBS_SHARED fltk_SHARED ${OPENGL_LIBRARIES})
+  else ()
+    set (UNITTEST_LIBS_SHARED fltk_gl_SHARED fltk_SHARED ${OPENGL_LIBRARIES})
+  endif ()
 else ()
   set (UNITTEST_LIBS fltk)
   set (UNITTEST_LIBS_SHARED fltk_SHARED)