FIX: Extra New Line Added to Debug Output in Visual Debugger

The information in this article applies to:

• The Visual Workbench Integrated Debugger

      - Microsoft Visual C++ 32-bit Edition, version 1.0
  

SYMPTOMS

When using the Visual Workbench debugger, a new line is inserted in the debugging output window every time debugging information is output through the CDumpContext insertion operator or OutputDebugString(). This interferes with formatting done for the debug output.

CAUSE

A new line is inserted by the debugger after every call to the Windows 3.1 application programming interface (API) function OutputDebugString(). In the Microsoft Foundation Classes (MFC), the insertion operator (<<) for CDumpContext eventually maps to a call to OutputDebugString(), so every invocation of << for a CDumpContext object also introduces a new line in the output window.

RESOLUTION

The following are three suggested workarounds:

• Use the WinDbg debugger that ships with the Microsoft Win32 Software Development Kit (SDK) for Windows NT. WinDbg does not insert uncalled for new lines into the debugging output.
• Consolidate debugging output into strings that can be displayed with a single call to OutputDebugString or with a single insertion into the dump context.
• Add additional lines of debugging information to indicate the beginning and end of a sequence of debugging output. For example,

     void CPerson::Dump( CDumpContext &dc ) const
      {
         dc << "Begin dump of CPerson object";  // identify dump start
         CObject::Dump( dc );
         dc << "Name: " << m_name;
         dc << "Age: " << m_years;
         dc << "End dump of CPerson object";    // identify dump end
      }
  
  

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. This problem was corrected in Visual C++ 2.0.

MORE INFORMATION

The following code fragment demonstrates the problem that occurs when calling OutputDebugString directly. The output that would normally appear on the same line actually displays over three lines:

Code

   OutputDebugString("This");
   OutputDebugString("output");
   OutputDebugString("takes three lines.\n");

Output

   This
   output
   takes three lines.

   void CPerson::Dump( CDumpContext &dc ) const
   {
      CObject::Dump( dc );
      dc << m_name << " is ";
      dc << m_years << " years old.\n";
   }

   a
   CObject
    at
   $18FC80

   FirstName LastName
    is
   30
    years old.

   a CObject at $3917477E FirstName LastName is 30 years old.