Let’s hope you never need to do this, but if you are forced to debug code written in C++\/CX, and you have a C++\/CX delegate and want to know what it is, well, here goes.<\/p>\n
0:005> dps 0x00000295`0d3a0ab0\r\n00000295`0d3a0ab0 00007ff9`c0238fd8 contoso!RoutedEventHandler::`vftable'\r\n00000295`0d3a0ab8 00007ff9`c0238f98 contoso!RoutedEventHandler::`vftable'\r\n00000295`0d3a0ac0 00007ff9`c0238f68 contoso!RoutedEventHandler::`vftable'\r\n00000295`0d3a0ac8 00000295`7d9f8ee0\r\n00000295`0d3a0ad0 ffffffff`ffffffff\r\n00000295`0d3a0ad8 00007ff9`c0252f08 contoso!`RoutedEventHandler<Widget,\r\n void (Widget::*)(Object ^,RoutedEventArgs ^)>'::\r\n `2'::__abi_PointerToMemberWeakRefCapture::`vftable'\r\n00000295`0d3a0ae0 00000295`469826e0\r\n00000295`0d3a0ae8 00007ff9`bfff2e80 contoso!Widget::OnColorChanged\r\n<\/pre>\nThe object starts with some vtables and other bookkeeping. But the interesting thing is the next vtable, because that one tells you what kind of delegate you have.<\/p>\n
In this case, it’s a vtable for a “pointer to member weak ref capture”, which tells us that our delegate is a weak pointer plus a pointer to member function.<\/p>\n
The next two pointers are the weak reference and the member function pointer.<\/p>\n
Most C++\/CX delegates are of the “weak pointer plus method pointer” variety, but the other flavor is the “functor”, where the handler is an arbitrary object that supports the function call operator.<\/p>\n
For example, a delegate that refers to a static method looks like this:<\/p>\n
0:000> dps 08062190\r\n08062190 0116a2f4 contoso!RoutedEventHandler::`vftable'\r\n08062194 0116a310 contoso!RoutedEventHandler::`vftable'\r\n08062198 0116a334 contoso!RoutedEventHandler::`vftable'\r\n0806219c 08068a10\r\n080621a0 ffffffff\r\n080621a4 0116a378 contoso!__abi_FunctorCapture<\r\n void (__cdecl*)(Object ^,RoutedEventArgs ^),\r\n void,\r\n Object ^,\r\n RoutedEventArgs ^>::`vftable'\r\n080621a8 00f9371c contoso!OnColorChanged\r\n<\/pre>\nThe vtable in position 5 says that this is a functor that captured a plain old function pointer, and the plain old function pointer comes immediately after: It’s
contoso!OnColorChanged<\/code>.<\/p>\nFor a class that supports the function call operator, you get a customized function for that class. In this example, the class is a lambda:<\/p>\n
08062240 0116a2f4 contoso!RoutedEventHandler::`vftable'\r\n08062244 0116a310 contoso!RoutedEventHandler::`vftable'\r\n08062248 0116a334 contoso!RoutedEventHandler::`vftable'\r\n0806224c 080689b0\r\n08062250 ffffffff\r\n08062254 0116a388 contoso!__abi_FunctorCapture<\r\n <lambda_484c5c4112f278281e0294b32780c5b6>,\r\n void,\r\n Object ^,\r\n RoutedEventArgs ^>::`vftable'\r\n08062258 08053480 \/\/ lambda contents start here\r\n0806225c 00000000\r\n<\/pre>\nIf the lambda is large (bigger than than 16 pointers), then it is stored in a separate memory allocation. You can find a pointer to the wrapper for the captured lambda 16 pointers later:<\/p>\n
07a2c2f0 00e57324 contoso!RoutedEventHandler::`vftable'\r\n07a2c2f4 00e57340 contoso!RoutedEventHandler::`vftable'\r\n07a2c2f8 00e57364 contoso!RoutedEventHandler::`vftable'\r\n07a2c2fc 07a36278\r\n07a2c300 ffffffff\r\n07a2c304 00000000 (unused slot 0)\r\n07a2c308 00000000 (unused slot 1)\r\n07a2c30c 00000000 (unused slot 2)\r\n07a2c310 00000000 (unused slot 3)\r\n07a2c314 00000000 (unused slot 4)\r\n07a2c318 00000000 (unused slot 5)\r\n07a2c31c 00000000 (unused slot 6)\r\n07a2c320 00000000 (unused slot 7)\r\n07a2c324 00000000 (unused slot 8)\r\n07a2c328 00000000 (unused slot 9)\r\n07a2c32c 00000000 (unused slot 10)\r\n07a2c330 00000000 (unused slot 11)\r\n07a2c334 00000000 (unused slot 12)\r\n07a2c338 00000000 (unused slot 13)\r\n07a2c33c 00000000 (unused slot 14)\r\n07a2c340 00000000 (unused slot 15)\r\n07a2c344 01212a48 \/\/ pointer to functor\r\n\r\n01212a48 00e57388 contoso!__abi_FunctorCapture<\r\n <lambda_51d3f9ef4e98c0ae34c7116adc4d714e>,\r\n void,\r\n Object ^,\r\n RoutedEventArgs ^>::`vftable'\r\n01212a4c 07a1f3d0 \/\/ lambda contents start here\r\n01212a50 00000000\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"If you ever have to debug one of these things.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-103362","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
If you ever have to debug one of these things.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/103362","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=103362"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/103362\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=103362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=103362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=103362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}