{"id":112062,"date":"2026-02-13T07:00:00","date_gmt":"2026-02-13T15:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=112062"},"modified":"2026-02-13T10:17:52","modified_gmt":"2026-02-13T18:17:52","slug":"20260213-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20260213-00\/?p=112062","title":{"rendered":"How can I distinguish between the numeric keypad 0 and the top-row 0 in the WM_CHAR<\/CODE> message?"},"content":{"rendered":"

Last time, we looked at how to distinguish the numeric keypad 0 and the top-row 0 in the WM_KEY\u00adDOWN<\/code> message<\/a>. We may as well look at the analogous table for WM_CHAR<\/code>.<\/p>\n\n\n\n\n\n\n\n
Event<\/th>\nwParam<\/th>\nExtended?<\/th>\n<\/tr>\n
Numpad0 with NumLock on<\/td>\nVK_0<\/tt><\/td>\n0<\/td>\n<\/tr>\n
Numpad0 with NumLock off<\/td>\n(no WM_CHAR<\/code>)<\/td>\n<\/tr>\n
Ins<\/kbd> key<\/td>\n(no WM_CHAR<\/code>)<\/td>\n<\/tr>\n
0 on top row<\/td>\nVK_0<\/tt><\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

I got the name VK_0<\/code> from this comment block in winuser.h<\/tt>.<\/p>\n

\/*\r\n * VK_0 - VK_9 are the same as ASCII '0' - '9' (0x30 - 0x39)\r\n * 0x3A - 0x40 : unassigned\r\n * VK_A - VK_Z are the same as ASCII 'A' - 'Z' (0x41 - 0x5A)\r\n *\/\r\n<\/pre>\n
Uh-oh. The extended bit doesn’t distinguish between the two. They both show up as VK_0<\/code>, non-extended.<\/p>\n
What changes is something not in the above table: The scan code.<\/p>\n
So let’s convert the scan code back to a virtual key.<\/p>\n
auto vk_from_scan = MapVirtualKey((lParam >> 16) & 0xFF, MAPVK_VSC_TO_VK);\r\n<\/pre>\n\n\n\n\n\n\n\n
Event<\/th>\nwParam<\/th>\nExtended?<\/th>\nvk_from_scan<\/tt><\/th>\n<\/tr>\n
Numpad0 with NumLock on<\/td>\nVK_0<\/tt><\/td>\n0<\/td>\nVK_INSERT<\/tt><\/td>\n<\/tr>\n
Numpad0 with NumLock off<\/td>\n(no WM_CHAR<\/code>)<\/td>\n<\/tr>\n
Ins<\/kbd> key<\/td>\n(no WM_CHAR<\/code>)<\/td>\n<\/tr>\n
0 on top row<\/td>\nVK_0<\/tt><\/td>\n0<\/td>\nVK_0<\/tt><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
So we can infer which zero was pressed by taking the scan code, mapping it to a virtual key, and seeing whether it’s the Ins<\/kbd> key (from the numeric keypad) or the 0<\/kbd> key (from the top row).<\/p>\n
But wait, we’re not done yet.<\/p>\n
There are ways to type the character 0<\/tt> without using the numeric keypad or the top row. For example, you can hold the Alt<\/kbd> key and then type 4<\/kbd>,8<\/kbd> on the numeric keypad, and that will type a 0<\/tt>. I tried it out, and the vk_from_scan<\/code> was VK_MENU<\/code>, which is the virtual key code for the Alt<\/kbd> key. Another way of entering a 0<\/tt> is by using an input method editor (IME). Or there might be a custom keyboard layout that generates a 0<\/tt> through some wacky chord sequence.<\/p>\n
Therefore, if the vk_from_scan<\/code> is neither VK_INSERT<\/code> nor VK_0<\/code>, you have to conclude that the 0<\/tt> was entered by some means other than the numeric keypad or the top row.<\/p>\n","protected":false},"excerpt":{"rendered":"
See if it matches the scan code.<\/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-112062","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
See if it matches the scan code.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/112062","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=112062"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/112062\/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=112062"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=112062"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=112062"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}