GetShortField function (wdbgexts.h)

Article
10/21/2021

The GetShortField function reads the value of a member in a structure if its size is less than or equal to 8 bytes, or initializes a structure so it can be read later. This function is not intended to be used directly; InitTypeRead or InitTypeReadPhysical and ReadField should be used instead.

Syntax

ULONG64 GetShortField(
  [in] IN ULONG64 TypeAddress,
  [in] IN LPCSTR  Name,
  [in] IN USHORT  StoreAddress
);

Parameters

[in] TypeAddress

The meaning of this parameter depends on the value of StoreAddress.

If StoreAddress is non-zero:

Specifies the address of the structure in the target's memory. This address is used for subsequent calls when StoreAddress is zero.

If StoreAddress is zero:

TypeAddress is ignored. The value of TypeAddress from the last call when StoreAddress was non-zero is used to specify the address of the structure in the target's memory.

[in] Name

The meaning of this parameter depends on the value of StoreAddress.

If StoreAddress is non-zero:

Specifies the name of the type of the structure at TypeAddress.

If StoreAddress is zero:

Specifies the name of the member in the structure to read. The address and type of the structure are remembered from a previous call to this function with StoreAddress not equal to zero. Submembers can be specified by using a period-separated path, for example, "myfield.mysubfield".

[in] StoreAddress

Specifies the mode of this function.

If StoreAddress is non-zero:

Causes this function to initialize a structure for reading its members. The address and type name for the structure is remembered.

If the bit value 0x2 is set in StoreAddress, the address TypeAddress is considered a physical address; otherwise, it is considered a virtual address.

If StoreAddress is zero:

Causes this function to read a member from a previously initialized structure.

Return value

Return code	Description
*If StoreAddress* is non-zero:**	If the function succeeds, it returns the value zero. If the function fails because the caller passed a zero value as TypeAddress, it returns the value MEMORY_READ_ERROR (defined in Wdbgexts.h). If the function fails for any other reason, it returns an IG_DUMP_SYMBOL_INFO error code.
*If StoreAddress* is zero:**	If the function succeeds, it returns the value of the specified field in the previously initialized structure. The structure is the one initialized in a previous call to GetShortField. The field is the one specified by the Name parameter of the current call to GetShortField. The return value is cast to ULONG64. If the function fails, it returns the value zero.

Remarks

When GetShortField is called with a nonzero StoreAddress value, it initializes the structure located at the address specified by TypeAddress. Only one structure can be initialized at a time. If GetShortField is called more than once with a nonzero StoreAddress value, only the structure specified in the most recent call is initialized. When GetShortField is called with StoreAddress equal to zero, it accesses the most recently initialized structure, reads in that structure the field specified by Name, and returns the value of that field.

This function does not need to be called directly. The macros InitTypeRead and InitTypeReadPhysical call this function with StoreAddress non-zero to prepare a structure for reading its members. The macro ReadField calls this function with StoreAddress (and TypeAddress) equal to zero, to read members from the structure.

Note because this function stores the TypeAddress and Name by using static local variables, and because this function is defined in WdbgExts.h, the C pre-processor will create a new instance of this function for each DLL, and TypeAddress and Name will only be available within a single source file. In other words, the structure must be initialized in the same source file from which the members are read.

The ReadField and ReadFieldStr macros read a field whose size is less than 8 bytes from a structure initialized with InitTypeRead or InitTypeReadPhysical.

#define ReadField(Field) \
    GetShortField(0, #Field, 0)

#define ReadFieldStr(FieldStr) \
    GetShortField(0, FieldStr, 0)

Parameters

Field FieldStr

Return Value

If this macro succeeds, it returns the value of the specified field in the previously initialized structure. The structure is the one initialized in a previous call to InitTypeRead, InitTypeStrRead, InitTypeReadPhysical, InitTypeStrReadPhysical, or GetShortField. The field is the one specified by the Field or FieldStr parameter of ReadField. The return value is cast to ULONG64. If the function fails, it returns the value zero.

The parameter Field is the name of the member. For ReadField, the C pre-processor will turn the parameter into a string. For ReadFieldStr, Field is expected to already be an ASCII string. For example, the following two commands are identical and read the same member from a previously initialized structure:

ReadField( myField );
ReadFieldStr( "myField" );

Submembers can be read by using a period-separated path, for example, "myField.mySubfield".

Note Because these macros use the GetShortField function, they must be called from the same source code file as the macros that initialize the structure for reading. For more details, see GetShortField.

If you are writing a WdbgExts extension, include wdbgexts.h. If you are writing a DbgEng extension that calls this function, include wdbgexts.h before dbgeng.h (see Writing DbgEng Extension Code for details).

The InitTypeRead macro initializes a structure so that its members can be read using ReadField.

#define InitTypeRead(
    Addr,
    Type
);

Parameters

Addr

Specifies the address of the structure in the target's virtual memory.

Type

Specifies the name of the type of the structure. The C pre-processor will turn Type into a string.

Returns value

If this macro succeeds, it returns the value zero. If it fails because the caller passed a zero value as Addr, it returns the value MEMORY_READ_ERROR (defined in Wdbgexts.h). If it fails for any other reason, it returns an IG_DUMP_SYMBOL_INFO error code.

The InitTypeReadPhysical and InitTypeStrReadPhysical macros initialize a structure in physical memory so that its members can be read using ReadField.

#define InitTypeReadPhysical(
    Addr,
    Type,
    TypeStr
);

Parameters

Addr

Specifies the address of the structure in the target's physical memory.

Type

Specifies the name of the type of the structure. The C pre-processor will turn Type into a string.

TypeStr

Specifies the name of the type of the structure. TypeStr is expected to be an ASCII string.

Returns value

The InitTypeRead macro initializes a structure so that its members can be read using ReadField.

#define InitTypeRead(
    Addr,
    TypeStr
);

Parameters

Addr

Specifies the address of the structure in the target's virtual memory.

Type

Specifies the name of the type of the structure. TypeStr is expected to be an ASCII string.

Returns value

Requirements

Requirement	Value
Target Platform	Desktop
Header	wdbgexts.h (include Wdbgexts.h, Dbgeng.h)

GetShortField function (wdbgexts.h)

Syntax

Parameters

If StoreAddress is non-zero:

If StoreAddress is zero:

If StoreAddress is non-zero:

If StoreAddress is zero:

If StoreAddress is non-zero:

If StoreAddress is zero:

Return value

Remarks

Parameters

Return Value

Requirements

See also

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