{"id":109342,"date":"2024-01-31T07:00:00","date_gmt":"2024-01-31T15:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=109342"},"modified":"2024-01-31T05:54:21","modified_gmt":"2024-01-31T13:54:21","slug":"20240131-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20240131-00\/?p=109342","title":{"rendered":"How can I add an environment variable to a process launched via Shell­Execute­Ex<\/CODE> or IContext­Menu<\/CODE>?"},"content":{"rendered":"

The Shell\u00adExecute\u00adEx<\/code> function and IContext\u00adMenu<\/code> interface provide the caller a number of places to customize how the execution occurs by allowing the call to pass a “site” which Shell\u00adExecute\u00adEx<\/code>\/IContext\u00adMenu<\/code> will access at various points in the execution process.<\/p>\n

Today we’ll demonstrate this technique by adding environment variables to processes launched via Shell\u00adExecute\u00adEx<\/code> and IContext\u00adMenu<\/code>.<\/p>\n

The ICreating\u00adProcess<\/code> interface is used by Shell\u00adExecute\u00adEx<\/code>. and IContext\u00adMenu<\/code> to allow the caller to customize how processes are created. The extension point is obtained by querying the site for SID_Execute\u00adCreating\u00adProcess<\/code> and requesting an ICreating\u00adProcess<\/code>. If one is produced, then the system calls the OnCreating<\/code> method with an object that allows the creation to be customized.<\/p>\n

Today’s C++ COM library is (rolls dice) C++\/WinRT.<\/p>\n

struct AddEnvironmentVariableSite :\r\n    winrt::implements<AddEnvironmentVariableSite,\r\n        ::IServiceProvider,\r\n        ::ICreatingProcess>\r\n{\r\n    IFACEMETHOD(QueryService)\r\n        (REFGUID service, REFIID riid, void** ppv)\r\n    {\r\n        if (service == SID_ExecuteCreatingProcess)\r\n        {\r\n            return this->QueryInterface(riid, ppv);\r\n        }\r\n        else\r\n        {\r\n            *ppv = nullptr;\r\n            return E_NOTIMPL;\r\n        }\r\n    }\r\n\r\n    IFACEMETHOD(OnCreating)(ICreateProcessInputs* inputs)\r\n    {\r\n        return inputs->SetEnvironmentVariable(\r\n            L\"EXTRAVARIABLE\", L\"Bonus\");\r\n    }\r\n};\r\n<\/pre>\n
This site responds to SID_Execute\u00adCreating\u00adProcess<\/code> by returning itself, and it implements ICreating\u00adProcess<\/code> by having its OnCreating<\/code> method set an environment variable called EXTRAVARIABLE<\/code> with a value of Bonus<\/code>. Since that is the only thing we do, we can just return the result of Set\u00adEnvironment\u00adVariable()<\/code> as our own return value. If you intend to add multiple environment variables, you would check the return value of each call to Set\u00adEnvironment\u00adVariable()<\/code>.<\/p>\n
In general, your custom site would be part of a so-called “site chain” and forward any unhandled services to your own site, so that an outer site could respond to it.<\/p>\n
Here’s an example of how to use this special environment variable site in conjunction with Shell\u00adExecute\u00adEx<\/code>:<\/p>\n
BOOL Sample()\r\n{\r\n    SHELLEXECUTEINFO sei{ sizeof(sei) };\r\n    sei.lpFile = LR\"(C:\\Windows\\system32\\charmap.exe)\";\r\n    sei.nShow = SW_SHOWNORMAL;\r\n    auto site = winrt::make_self<AddEnvironmentVariableSite>();<\/span>\r\n    sei.hInstApp = reinterpret_cast<HINSTANCE>(site.get());    <\/span>\r\n    sei.fMask = SEE_MASK_FLAG_HINST_IS_SITE;                   <\/span>\r\n    return ShellExecuteEx(&sei);\r\n}\r\n<\/pre>\n
To pass a site to Shell\u00adExecute\u00adEx<\/code>, we put it in the hInstApp<\/code> member and set the SEE_MASK_FLAG_HINST_IS_SITE<\/code> flag to say “If you look at the hInstApp<\/code>, you’ll find a site!”\u00b9<\/p>\n
For context menus, we explicitly set our custom site as the context menu’s site. Building on  our original sample for hosting an IContext\u00adMenu<\/code><\/a>:<\/p>\n
void OnContextMenu(HWND hwnd, HWND hwndContext, UINT xPos, UINT yPos)\r\n{\r\n  IContextMenu *pcm;\r\n  if (SUCCEEDED(GetUIObjectOfFile(hwnd, L\"C:\\\\Windows\\\\clock.avi\",\r\n                   IID_IContextMenu, (void**)&pcm))) {\r\n    HMENU hmenu = CreatePopupMenu();\r\n    if (hmenu) {\r\n      if (SUCCEEDED(pcm->QueryContextMenu(hmenu, 0,\r\n                             SCRATCH_QCM_FIRST, SCRATCH_QCM_LAST,\r\n                             CMF_NORMAL))) {\r\n        CMINVOKECOMMANDINFO info = { 0 };\r\n        info.cbSize = sizeof(info);\r\n        info.hwnd = hwnd;\r\n        info.lpVerb = \"play\";\r\n        auto site = winrt::make_self<AddEnvironmentVariableSite>();<\/span>\r\n        IUnknown_SetSite(pcm, site.get());                         <\/span>\r\n        pcm->InvokeCommand(&info);\r\n        IUnknown_SetSite(pcm, nullptr);                            <\/span>\r\n      }\r\n      DestroyMenu(hmenu);\r\n    }\r\n    pcm->Release();\r\n  }\r\n}\r\n<\/pre>\n
(I’m ignoring the fact that winrt::make_self<\/code> can throw an exception which results in a memory leak in the sample code above.)<\/p>\n
\u00b9 This is admitted a rather ugly way to pass a site, but the ability to add a site was retrofitted onto the existing structure, so we had to hide it in an other-wise unused input member.<\/p>\n","protected":false},"excerpt":{"rendered":"
Hooking into the way the Windows shell launches processes.<\/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-109342","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Hooking into the way the Windows shell launches processes.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109342","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=109342"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109342\/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=109342"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=109342"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=109342"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}