The new C++ standard defines a new keyword, static_assert<\/b>, that is already available in Visual Studio 2010 CTP. This new feature allows introducing compile time asserts. It takes an expression that can evaluate to bool and a string. If the expression evaluates to false, the compiler issues an error with the given string literal. If the expression evaluates to true, static_assert has no effect.<\/p>\n
Here is an example for using static_assert. Suppose you want to create a template vector class, but you don’t want to allow vectors with a size smaller than 4. Then you can use a static assertion to enforce that.<\/p>\n
\r\ntemplate < class T, int Size >\r\nclass Vector\r\n{\r\n static_assert(Size > 3, \"Vector size is too small!\");\r\n\r\n T m_values[Size];\r\n};\r\n\r\nint _tmain(int argc, _TCHAR* argv[])\r\n{\r\n Vector< int, 4 > four;\r\n Vector< short, 2 > two;\r\n\r\n return 0;\r\n}\r\n<\/pre>\nCompiling this program triggers an error at the second declaration.<\/p>\n
\r\nc:\\projects\\cpp_demo\\cpp_demo.cpp(17) : error C2338: Vector size is too small!\r\n c:\\projects\\cpp_demo\\cpp_demo.cpp(33) : see reference to class template instantiation 'Vector< T,Size >' \r\n being compiled\r\n with\r\n [\r\n T=short,\r\n Size=2\r\n ]\r\n<\/pre>\nMost of the use cases for this feature, in my opinion, would be to test on the size of different types. For instance this sample is taken from the C++0x draft.<\/p>\n
\r\nstatic_assert(sizeof(long) >= 8, \"64-bit code generation required for this library.\");\r\n<\/pre>\nTo me, static_assert looks like a niche feature. It would have been great if this could be used together with some other features to enfore compile time constraints on types. For instance, I want to restrict the possible types for a template class or function to only those that are derived from IListener (a fictive class).<\/p>\n
\r\ntemplate < class T >\r\nclass foo\r\n{\r\n static_assert(convertible_from< IListener >(decltype(T)), \"Type is not a correct type!\");\r\n};\r\n<\/pre>\nPerhaps a future standard version will offer support for such things.<\/p>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
The new C++ standard defines a new keyword, static_assert, that is already available in Visual Studio 2010 CTP. This new feature allows introducing compile time asserts. It takes an expression that can evaluate to bool and a string. If the expression evaluates to false, the compiler issues an error with the given string literal. If … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7,20,10],"tags":[88,451,73,90,87,89],"class_list":["post-184","post","type-post","status-publish","format-standard","hentry","category-c","category-ctps-betas","category-visual-studio","tag-assert","tag-c","tag-c0x","tag-ctp","tag-static_assert","tag-vs2010"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t