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Header Annotations

[This topic describes the annotations supported in the Windows headers through Windows 7. If you are developing for Windows 8, you should use the annotations described in SAL Annotations.]]

Header annotations describe how a function uses its parameters and return value. These annotations have been added to many of the Windows header files to help you ensure that you are calling the Windows API correctly. If you enable code analysis, which is available starting with the Visual Studio 2005, the compiler will produce level 6000 warnings if you are not calling these functions per the usage described through the annotations. You can also add these annotations in your own code to ensure that it is being called correctly. To enable code analysis in Visual Studio, see the documentation for your version of Visual Studio.

These annotations are defined in Specstrings.h. They are built on primitives that are part of the Standard Annotation Language (SAL) and implemented using _declspec("SAL_*").

There are two classes of annotations: buffer annotations and advanced annotations.

Buffer Annotations

Buffer annotations describe how functions use their pointers and can be used to detect buffer overruns. Each parameter may use zero or one buffer annotation. A buffer annotation is constructed with a leading underscore and the components described in the following sections.

Buffer sizeDescription

(size)

Specifies the total size of the buffer. Use with _bcount and _ecount; do not use with _part. This value is the accessible space; it may be less than the allocated space.

(size,length)

Specifies the total size and initialized length of the buffer. Use with _bcount_part and _ecount_part. The total size may be less than the allocated space.

 

Buffer size unitsDescription

_bcount

The buffer size is in bytes.

_ecount

The buffer size is in elements.

 

DirectionDescription

_in

The function reads from the buffer. The caller provides the buffer and initializes it.

_inout

The function both reads from and writes to buffer. The caller provides the buffer and initializes it. If used with _deref, the buffer may be reallocated by the function.

_out

The function writes to the buffer. If used on the return value or with _deref, the function provides the buffer and initializes it. Otherwise, the caller provides the buffer and the function initializes it.

 

IndirectionDescription

_deref

Dereference the parameter to obtain the buffer pointer. This parameter may not be NULL.

_deref_opt

Dereference the parameter to obtain the buffer pointer. This parameter can be NULL.

 

InitializationDescription

_full

The function initializes the entire buffer. Use only with output buffers.

_part

The function initializes part of the buffer, and explicitly indicates how much. Use only with output buffers.

 

Required or optional bufferDescription

_opt

This parameter can be NULL.

 

The following example shows the annotations for the GetModuleFileName function. The hModule parameter is an optional input parameter . The lpFilename parameter is an output parameter; its size in characters is specified by the nSize parameter and its length includes the null-terminating character. The nSize parameter is an input parameter.


DWORD
WINAPI
GetModuleFileName(
    __in_opt HMODULE hModule,
    __out_ecount_part(nSize, return + 1) LPTSTR lpFilename,
    __in DWORD nSize
    );


The following are the annotations defined in Specstrings.h. Use the information in the tables above to interpret their meaning.

__bcount(size)
__bcount_opt(size)
__deref_bcount(size)
__deref_bcount_opt(size)
__deref_ecount(size)
__deref_ecount_opt(size)
__deref_in
__deref_in_bcount(size)
__deref_in_bcount_opt(size)
__deref_in_ecount(size)
__deref_in_ecount_opt(size)
__deref_in_opt
__deref_inout
__deref_inout_bcount(size)
__deref_inout_bcount_full(size)
__deref_inout_bcount_full_opt(size)
__deref_inout_bcount_opt(size)
__deref_inout_bcount_part(size,length)
__deref_inout_bcount_part_opt(size,length)
__deref_inout_ecount(size)
__deref_inout_ecount_full(size)
__deref_inout_ecount_full_opt(size)
__deref_inout_ecount_opt(size)
__deref_inout_ecount_part(size,length)
__deref_inout_ecount_part_opt(size,length)
__deref_inout_opt
__deref_opt_bcount(size)
__deref_opt_bcount_opt(size)
__deref_opt_ecount(size)
__deref_opt_ecount_opt(size)
__deref_opt_in
__deref_opt_in_bcount(size)
__deref_opt_in_bcount_opt(size)
__deref_opt_in_ecount(size)
__deref_opt_in_ecount_opt(size)
__deref_opt_in_opt
__deref_opt_inout
__deref_opt_inout_bcount(size)
__deref_opt_inout_bcount_full(size)
__deref_opt_inout_bcount_full_opt(size)
__deref_opt_inout_bcount_opt(size)
__deref_opt_inout_bcount_part(size,length)
__deref_opt_inout_bcount_part_opt(size,length)
__deref_opt_inout_ecount(size)
__deref_opt_inout_ecount_full(size)
__deref_opt_inout_ecount_full_opt(size)
__deref_opt_inout_ecount_opt(size)
__deref_opt_inout_ecount_part(size,length)
__deref_opt_inout_ecount_part_opt(size,length)
__deref_opt_inout_opt
__deref_opt_out
__deref_opt_out_bcount(size)
__deref_opt_out_bcount_full(size)
__deref_opt_out_bcount_full_opt(size)
__deref_opt_out_bcount_opt(size)
__deref_opt_out_bcount_part(size,length)
__deref_opt_out_bcount_part_opt(size,length)
__deref_opt_out_ecount(size)
__deref_opt_out_ecount_full(size)
__deref_opt_out_ecount_full_opt(size)
__deref_opt_out_ecount_opt(size)
__deref_opt_out_ecount_part(size,length)
__deref_opt_out_ecount_part_opt(size,length)
__deref_opt_out_opt
__deref_out
__deref_out_bcount(size)
__deref_out_bcount_full(size)
__deref_out_bcount_full_opt(size)
__deref_out_bcount_opt(size)
__deref_out_bcount_part(size,length)
__deref_out_bcount_part_opt(size,length)
__deref_out_ecount(size)
__deref_out_ecount_full(size)
__deref_out_ecount_full_opt(size)
__deref_out_ecount_opt(size)
__deref_out_ecount_part(size,length)
__deref_out_ecount_part_opt(size,length)
__deref_out_opt
__ecount(size)
__ecount_opt(size)
__in
__in_bcount(size)
__in_bcount_opt(size)
__in_ecount(size)
__in_ecount_opt(size)
__in_opt
__inout
__inout_bcount(size)
__inout_bcount_full(size)
__inout_bcount_full_opt(size)
__inout_bcount_opt(size)
__inout_bcount_part(size,length)
__inout_bcount_part_opt(size,length)
__inout_ecount(size)
__inout_ecount_full(size)
__inout_ecount_full_opt(size)
__inout_ecount_opt(size)
__inout_ecount_part(size,length)
__inout_ecount_part_opt(size,length)
__inout_opt
__out
__out_bcount(size)
__out_bcount_full(size)
__out_bcount_full_opt(size)
__out_bcount_opt(size)
__out_bcount_part(size,length)
__out_bcount_part_opt(size,length)
__out_ecount(size)
__out_ecount_full(size)
__out_ecount_full_opt(size)
__out_ecount_opt(size)
__out_ecount_part(size,length)
__out_ecount_part_opt(size,length)
__out_opt

Advanced Annotations

Advanced annotations provide additional information about the parameter or return value. Each parameter or return value may use zero or one advanced annotation.

AnnotationDescription

__blocksOn(resource)

The functions blocks on the specified resource.

__callback

The function can be used as a function pointer.

__checkReturn

Callers must check the return value.

__format_string

The parameter is a string that contains printf-style % markers.

__in_awcount(expr,size)

If the expression is true at exit, the size of the input buffer is specified in bytes. If the expression is false, the size is specified in elements.

__nullnullterminated

The buffer may be accessed up to and including the first sequence of two null characters or pointers.

__nullterminated

The buffer may be accessed up to and including the first null character or pointer.

__out_awcount(expr,size)

If the expression is true at exit, the size of the output buffer is specified in bytes. If the expression is false, the size is specified in elements.

__override

Specifies C#-style override behavior for virtual methods.

__reserved

The parameter is reserved for future use and must be zero or NULL.

__success(expr)

If the expression is true at exit, the caller can rely on all guarantees specified by other annotations. If the expression is false, the caller cannot rely on the guarantees. This annotation is automatically added to functions that return an HRESULT value.

__typefix(ctype)

Treat the parameter as the specified type rather than its declared type.

 

The following examples show the buffer and advanced annotations for the DeleteTimerQueueTimer, FreeEnvironmentStrings, and UnhandledExceptionFilter functions.


__checkReturn
BOOL
WINAPI
DeleteTimerQueueTimer(
    __in_opt HANDLE TimerQueue,
    __in     HANDLE Timer,
    __in_opt HANDLE CompletionEvent
    );

BOOL
WINAPI
FreeEnvironmentStrings(
    __in __nullnullterminated LPTCH
    );

__callback
LONG
WINAPI
UnhandledExceptionFilter(
    __in struct _EXCEPTION_POINTERS *ExceptionInfo
    );



Related topics

SAL Annotations
Walkthrough: Analyzing C/C++ Code for Defects

 

 

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