Debugging and Error Reporting Macros

These macros provide useful debugging and trace facilities.

_ATL_DEBUG_INTERFACES

Define this macro before including any ATL header files to trace all AddRef and Release calls on your components' interfaces to the output window.

#define _ATL_DEBUG_INTERFACES

Remarks

The trace output will appear as shown below:

ATL: QIThunk - 2008 AddRef : Object = 0x00d81ba0 Refcount = 1 CBug - IBug

The first part of each trace will always be ATL: QIThunk. Next is a value identifying the particular interface thunk being used. An interface thunk is an object used to maintain a reference count and provide the tracing capability used here. A new interface thunk is created on every call to QueryInterface except for requests for the IUnknown interface (in this case, the same thunk is returned every time to comply with COM's identity rules).

Next you'll see AddRef or Release indicating which method was called. Following that, you'll see a value identifying the object whose interface reference count was changed. The value traced is the this pointer of the object.

The reference count that is traced is the reference count on that thunk after AddRef or Release was called. Note that this reference count may not match the reference count for the object. Each thunk maintains its own reference count to help you fully comply with COM's reference-counting rules.

The final piece of information traced is the name of the object and the interface being affected by the AddRef or Release call.

Any interface leaks that are detected when the server shuts down and _Module.Term is called will be logged like this:

ATL: QIThunk - 2005 LEAK : Object = 0x00d81ca0 Refcount = 1 MaxRefCount = 1 CBug - IBug

The information provided here maps directly to the information provided in the previous trace statements, so you can examine the reference counts throughout the whole lifetime of an interface thunk. In addition, you get an indication of the maximum reference count on that interface thunk.

_ATL_DEBUG_QI

Writes all calls to QueryInterface to the output window.

#define _ATL_DEBUG_QI

Remarks

If a call to QueryInterface failed, the output window will display:

interface name - failed

ATLASSERT

The ATLASSERT macro performs the same functionality as the _ASSERTE macro found in the C run-time library.

ATLASSERT(booleanExpression);

Parameters

booleanExpression
Expression (including pointers) that evaluates to nonzero or 0.

Remarks

In debug builds, ATLASSERT evaluates booleanExpression and generates a debug report when the result is false.

Requirements

Header: atldef.h

ATLENSURE

This macro is used to validate parameters passed to a function.

ATLENSURE(booleanExpression);
ATLENSURE_THROW(booleanExpression, hr);

Parameters

booleanExpression
Specifies a boolean expression to be tested.

hr
Specifies an error code to return.

Remarks

These macros provide a mechanism to detect and notify the user of incorrect parameter usage.

The macro calls ATLASSERT and if the condition fails calls AtlThrow.

In the ATLENSURE case, AtlThrow is called with E_FAIL.

In the ATLENSURE_THROW case, AtlThrow is called with the specified HRESULT.

The difference between ATLENSURE and ATLASSERT is that ATLENSURE throws an exception in Release builds as well as in Debug builds.

Example

void MyImportantFunction(char* psz)
{
   ATLENSURE(NULL != psz);

   char mysz[64];
   strcpy_s(mysz, sizeof(mysz), psz);
}

Requirements

Header: afx.h

ATLTRACENOTIMPL

In debug builds of ATL, sends the string " funcname is not implemented" to the dump device and returns E_NOTIMPL.

ATLTRACENOTIMPL(funcname);

Parameters

funcname
[in] A string containing the name of the function that is not implemented.

Remarks

In release builds, simply returns E_NOTIMPL.

Example

ATLTRACENOTIMPL(_T("IOleControl::GetControlInfo"));   

Requirements

Header: atltrace.h

ATLTRACE

Reports warnings to an output device, such as the debugger window, according to the indicated flags and levels. Included for backward compatibility.

ATLTRACE(exp);

ATLTRACE(
    DWORD category,
    UINT  level,
    LPCSTR lpszFormat, ...);

Parameters

exp
[in] The string and variables to send to the output window or any application that traps these messages.

category
[in] Type of event or method on which to report. See the Remarks for a list of categories.

level
[in] The level of tracing to report. See the Remarks for details.

lpszFormat
[in] The formatted string to send to the dump device.

Remarks

See ATLTRACE2 for a description of ATLTRACE. ATLTRACE and ATLTRACE2 have the same behavior, ATLTRACE is included for backward compatibility.

ATLTRACE2

Reports warnings to an output device, such as the debugger window, according to the indicated flags and levels.

ATLTRACE2(exp);

ATLTRACE2(
    DWORD category,
    UINT level,
    LPCSTR lpszFormat,  ...);

Parameters

exp
[in] The string to send to the output window or any application that traps these messages.

category
[in] Type of event or method on which to report. See the Remarks for a list of categories.

level
[in] The level of tracing to report. See the Remarks for details.

lpszFormat
[in] The printf-style format string to use to create a string to send to the dump device.

Remarks

The short form of ATLTRACE2 writes a string to the debugger's output window. The second form of ATLTRACE2 also writes output to the debugger's output window, but is subject to the settings of the ATL/MFC Trace Tool (see ATLTraceTool Sample). For example, if you set level to 4 and the ATL/MFC Trace Tool to level 0, you will not see the message. level can be 0, 1, 2, 3, or 4. The default, 0, reports only the most serious problems.

The category parameter lists the trace flags to set. These flags correspond to the types of methods for which you want to report. The tables below list the valid trace flags you can use for the category parameter.

ATL Trace Flags

MFC Trace Flags

To declare a custom trace category, declare a global instance of the CTraceCategory class as follows:

CTraceCategory MY_CATEGORY(_T("MyCategoryName"), 1);

The category name, MY_CATEGORY in this example, is the name you specify to the category parameter. The first parameter is the category name that will appear in the ATL/MFC Trace Tool. The second parameter is the default trace level. This parameter is optional, and the default trace level is 0.

To use a user-defined category:

ATLTRACE2(MY_CATEGORY, 2, _T("a message in a custom category"));

To specify that you want to filter the trace messages, insert definitions for these macros into Stdafx.h before the #include <atlbase.h> statement.

Alternatively, you can set the filter in the preprocessor directives in the Property Pages dialog box. Click the Preprocessor tab and then insert the global into the Preprocessor Definitions edit box.

Atlbase.h contains default definitions of the ATLTRACE2 macros and these definitions will be used if you don't define these symbols before atlbase.h is processed.

In release builds, ATLTRACE2 compiles to (void) 0.

ATLTRACE2 limits the contents of the string to be sent to the dump device to no more than 1023 characters, after formatting.

ATLTRACE and ATLTRACE2 have the same behavior, ATLTRACE is included for backward compatibility.

Example

int i = 1;
ATLTRACE2(atlTraceGeneral, 4, "Integer = %d\n", i);
// Output: 'Integer = 1'

See also

Macros
Debugging and Error Reporting Global Functions