{"id":111890,"date":"2025-12-22T07:00:00","date_gmt":"2025-12-22T15:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=111890"},"modified":"2025-12-24T11:26:30","modified_gmt":"2025-12-24T19:26:30","slug":"all-the-other-cool-languages-have-try-finally-c-says-we-have-try-finally-at-home","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20251222-00\/?p=111890","title":{"rendered":"All the other cool languages have try<\/CODE>…finally<\/CODE>. C++ says “We have try<\/CODE>…finally<\/CODE> at home.”"},"content":{"rendered":"

Many languages\u00b9 that have exceptions also have a finally<\/code> clause, so you can write<\/p>\n

try {\r\n    \u27e6 stuff \u27e7\r\n} finally {\r\n    always();\r\n}\r\n<\/pre>\n
A quick checks shows that this control structure exists in Java, C#, Python, JavaScript, but not C++.<\/p>\n
C++ says, “We have try<\/code>…finally at home.”<\/p>\n
In C++, the way to get a block of code to execute when control leaves a block is to put it in a destructor, because destructors run when control leaves a block. This is the trick used by the Windows Implementation Library’s  wil::scope_exit<\/a> function: The lambda you provide is placed inside a custom object whose destructor runs the lambda.<\/p>\n
auto ensure_cleanup = wil::scope_exit([&] { always(); });\r\n\r\n\u27e6 stuff \u27e7\r\n<\/pre>\n
Although the principle is the same, there are some quirks in how each language treats the case where the finally<\/code> or destructor itself throws an exception.<\/p>\n
If control leaves the guarded block without an exception, then any uncaught exception that occurs in the finally<\/code> block or the destructor is thrown from the try<\/code> block. All the languages seem to agree on this.<\/p>\n
If control leaves the guarded block with an exception, and the finally<\/code> block or destructor also<\/i> throws an exception, then the behavior varies by language.<\/p>\n