description	Learn more about: Annotating function behavior
title	Annotating function behavior
ms.date	11/04/2016
ms.topic	conceptual
f1_keywords	_On_failure_ _Return_type_success_ _Always_ _Maybe_raises_SEH_exception_ _Raises_SEH_exception_ _Called_from_function_class_ _Function_class_ _Must_inspect_result_ _Success_ _Check_return_ _Use_decl_annotations_
ms.assetid	c0aa268d-6fa3-4ced-a8c6-f7652b152e61

Annotating function behavior

In addition to annotating function parameters and return values, you can annotate properties of the whole function.

Function annotations

The following annotations apply to the function as a whole and describe how it behaves or what it expects to be true.

Annotation	Description
_Called_from_function_class_(name)	Not intended to stand alone; instead, it is a predicate to be used with the _When_ annotation. For more information, see Specifying When and Where an Annotation Applies. The name parameter is an arbitrary string that also appears in a _Function_class_ annotation in the declaration of some functions. _Called_from_function_class_ returns nonzero if the function that is currently being analyzed is annotated by using _Function_class_ that has the same value of name; otherwise, it returns zero.
_Check_return_	Annotates a return value and states that the caller should inspect it. The checker reports an error if the function is called in a void context.
_Function_class_(name)	The name parameter is an arbitrary string that is designated by the user. It exists in a namespace that is distinct from other namespaces. A function, function pointer, or—most usefully—a function pointer type may be designated as belonging to one or more function classes.
_Raises_SEH_exception_	Annotates a function that always raises a structured exception handler (SEH) exception, subject to _When_ and _On_failure_ conditions. For more information, see Specifying When and Where an Annotation Applies.
_Maybe_raises_SEH_exception_	Annotates a function that may optionally raise an SEH exception, subject to _When_ and _On_failure_ conditions.
_Must_inspect_result_	Annotates any output value, including the return value, parameters, and globals. The analyzer reports an error if the value in the annotated object is not subsequently inspected. "Inspection" includes whether it is used in a conditional expression, is assigned to an output parameter or global, or is passed as a parameter. For return values, _Must_inspect_result_ implies _Check_return_.
_Use_decl_annotations_	May be used on a function definition (also known as a function body) in place of the list of annotations in the header. When _Use_decl_annotations_ is used, the annotations that appear on an in-scope header for the same function are used as if they are also present in the definition that has the _Use_decl_annotations_ annotation.

Success/failure annotations

A function can fail, and when it does, its results may be incomplete or differ from the results when the function succeeds. The annotations in the following list provide ways to express the failure behavior. To use these annotations, you must enable them to determine success; therefore, a _Success_ annotation is required. Notice that NTSTATUS and HRESULT already have a _Success_ annotation built into them; however, if you specify your own _Success_ annotation on NTSTATUS or HRESULT, it overrides the built-in annotation.

Annotation	Description
_Always_(anno_list)	Equivalent to anno_list _On_failure_(anno_list); that is, the annotations in anno_list apply whether or not the function succeeds.
_On_failure_(anno_list)	To be used only when _Success_ is also used to annotate the function—either explicitly, or implicitly through _Return_type_success_ on a typedef. When the _On_failure_ annotation is present on a function parameter or return value, each annotation in anno_list (anno) behaves as if it were coded as _When_(!expr, anno), where expr is the parameter to the required _Success_ annotation. This means that the implied application of _Success_ to all post-conditions does not apply for _On_failure_.
_Return_type_success_(expr)	May be applied to a typedef. Indicates that all functions that return that type and do not explicitly have _Success_ are annotated as if they had _Success_(expr). _Return_type_success_ cannot be used on a function or a function pointer typedef.
_Success_(expr)	expr is an expression that yields an rvalue. When the _Success_ annotation is present on a function declaration or definition, each annotation (anno) on the function and in post-condition behaves as if it were coded as _When_(expr, anno). The _Success_ annotation may be used only on a function, not on its parameters or return type. There can be at most one _Success_ annotation on a function, and it cannot be in any _When_, _At_, or _Group_. For more information, see Specifying When and Where an Annotation Applies.

See also

• Using SAL Annotations to Reduce C/C++ Code Defects
• Understanding SAL
• Annotating Function Parameters and Return Values
• Annotating Structs and Classes
• Annotating Locking Behavior
• Specifying When and Where an Annotation Applies
• Intrinsic Functions
• Best Practices and Examples