Be more conservative about QPDF_DLL_CLASS with mingw (fixes #799)

* Define it even though previous experiments have shown it to be
  unnecessary since it seems like it may be necessary after all
* Add QPDF_DLL_CLASS to QPDFObjectHelper and QPDFDocumentHelper in
  case there's some future unknown reason why someone may want to have
  them and/or in case it helps with the weird
  QPDFNameTreeObjectHelper problem.

3 files changed, 11 insertions, 6 deletions

diff --git a/include/qpdf/DLL.h b/include/qpdf/DLL.h
index 14cc5bae..257486b0 100644
--- a/include/qpdf/DLL.h
+++ b/include/qpdf/DLL.h
@@ -42,14 +42,16 @@
 #  define QPDF_DLL
 # endif
 # define QPDF_DLL_PRIVATE
-# define QPDF_DLL_CLASS
 #elif defined __GNUC__
 # define QPDF_DLL __attribute__((visibility("default")))
 # define QPDF_DLL_PRIVATE __attribute__((visibility("hidden")))
-# define QPDF_DLL_CLASS QPDF_DLL
 #else
 # define QPDF_DLL
 # define QPDF_DLL_PRIVATE
+#endif
+#ifdef __GNUC__
+# define QPDF_DLL_CLASS QPDF_DLL
+#else
 # define QPDF_DLL_CLASS
 #endif
 
@@ -87,6 +89,9 @@ for a more in-depth discussion.
     multi-platform and building both static and shared libraries that
     use the same headers, so we don't bother.
 
+  * If we don't export base classes with mingw, the vtables don't end
+    up in the DLL.
+
 * On Linux (and other similar systems):
 
   * Common compilers such as gcc and clang export all symbols into the
diff --git a/include/qpdf/QPDFDocumentHelper.hh b/include/qpdf/QPDFDocumentHelper.hh
index 55fe3c9c..e78788ab 100644
--- a/include/qpdf/QPDFDocumentHelper.hh
+++ b/include/qpdf/QPDFDocumentHelper.hh
@@ -36,7 +36,7 @@
 // introduced to allow creation of higher level helper functions
 // without polluting the public interface of QPDF.
 
-class QPDFDocumentHelper
+class QPDF_DLL_CLASS QPDFDocumentHelper
 {
   public:
     QPDF_DLL
@@ -45,7 +45,7 @@ class QPDFDocumentHelper
     {
     }
     QPDF_DLL
-    virtual ~QPDFDocumentHelper() = default;
+    virtual ~QPDFDocumentHelper();
     QPDF_DLL
     QPDF&
     getQPDF()
diff --git a/include/qpdf/QPDFObjectHelper.hh b/include/qpdf/QPDFObjectHelper.hh
index db3876ec..7f0f21ca 100644
--- a/include/qpdf/QPDFObjectHelper.hh
+++ b/include/qpdf/QPDFObjectHelper.hh
@@ -37,7 +37,7 @@
 // introduced to allow creation of higher level helper functions
 // without polluting the public interface of QPDFObjectHandle.
 
-class QPDFObjectHelper
+class QPDF_DLL_CLASS QPDFObjectHelper
 {
   public:
     QPDF_DLL
@@ -46,7 +46,7 @@ class QPDFObjectHelper
     {
     }
     QPDF_DLL
-    virtual ~QPDFObjectHelper() = default;
+    virtual ~QPDFObjectHelper();
     QPDF_DLL
     QPDFObjectHandle
     getObjectHandle()