How do I print to the debug output window in a Win32 app

Question

I ve got a win32 project that I ve loaded into Visual Studio 2005  I d like to be able to print things to the Visual Studio output window  but I can t for the life of me work out how  I ve tried  printf  and  cout  lt  lt   but my messages stay stubbornly unprinted   Is there some sort of special way to print to the Visual Studio output window

User · Answer

If you need to see the output of an existing program that extensively used printf w o changing the code  or with minimal changes  you can redefine printf as follows and add it to the common header  stdafx h     int print log const char  format             static char s printf buf 1024       va list args      va start args  format        vsnprintf s printf buf  sizeof s printf buf   format  args       va end args       OutputDebugStringA s printf buf       return 0      define printf format                 print log format    VA ARGS

User · Answer

If the project is a GUI project  no console will appear  In order to change the project into a console one you need to go to the project properties panel and set    In  linker- System- SubSystem  the value  Console   SUBSYSTEM CONSOLE   In  C C  - Preprocessor- Preprocessor Definitions  add the   CONSOLE  define   This solution works only if you had the classic  int main    entry point   But if you are like in my case  an openGL project   you don t need to edit the properties  as this works better   AllocConsole    freopen  CONIN     r  stdin   freopen  CONOUT     w  stdout   freopen  CONOUT     w  stderr     printf and cout will work as usual   If you call AllocConsole before the creation of a window  the console will appear behind the window  if you call it after  it will appear ahead   Update  freopen is deprecated and may be unsafe  Use freopen s instead   FILE  fp   AllocConsole    freopen s  amp fp   CONIN     r   stdin   freopen s  amp fp   CONOUT     w   stdout   freopen s  amp fp   CONOUT     w   stderr

User · Answer

You can use OutputDebugString  OutputDebugString is a macro that depending on your build options either maps to OutputDebugStringA char const   or OutputDebugStringW wchar t const    In the later case you will have to supply a wide character string to the function  To create a wide character literal you can use the L prefix   OutputDebugStringW L My output string       Normally you will use the macro version together with the  T macro like this   OutputDebugString  T  My output string        If you project is configured to build for UNICODE it will expand into   OutputDebugStringW L My output string       If you are not building for UNICODE it will expand into   OutputDebugStringA  My output string

User · Answer

I was looking for a way to do this myself and figured out a simple solution    I m assuming that you started a default Win32 Project  Windows application  in Visual Studio  which provides a  WinMain  function  By default  Visual Studio sets the entry point to  SUBSYSTEM WINDOWS   You need to first change this by going to   Project -  Properties -  Linker -  System -  Subsystem  And select  Console   SUBSYSTEM CONSOLE   from the drop-down list   Now  the program will not run  since a  main  function is needed instead of the  WinMain  function   So now you can add a  main  function like you normally would in C    After this  to start the GUI program  you can call the  WinMain  function from inside the  main  function   The starting part of your program should now look something like this    include  lt iostream gt   using namespace std      Main function for the console int main            Calling the wWinMain function to start the GUI program        Parameters         GetModuleHandle NULL  - To get a handle to the current instance        NULL - Previous instance is not needed        NULL - Command line parameters are not needed        1 - To show the window normally     wWinMain GetModuleHandle NULL   NULL NULL  1         system  pause        return 0        Function for entry into GUI program int APIENTRY wWinMain  In  HINSTANCE hInstance                        In opt  HINSTANCE hPrevInstance                        In  LPWSTR    lpCmdLine                        In  int       nCmdShow           This will display  Hello World  in the console as soon as the GUI begins      cout  lt  lt   Hello World   lt  lt  endl          Result of my implementation  Now you can use functions to output to the console in any part of your GUI program for debugging or other purposes

User · Answer

Consider using the VC   runtime Macros for Reporting  RPTN   and  RPTFN       You can use the  RPTn  and  RPTFn macros  defined in CRTDBG H  to   replace the use of printf statements for debugging  These macros   automatically disappear in your release build when  DEBUG is not   defined  so there is no need to enclose them in  ifdefs    Example     if  someVar  gt  MAX SOMEVAR         RPTF2  CRT WARN   In NameOfThisFunc                  someVar   d  otherVar   d n   someVar  otherVar        Or you can use the VC   runtime functions  CrtDbgReport   CrtDbgReportW directly       CrtDbgReport and  CrtDbgReportW can send the debug report to three different destinations  a debug report file  a debug monitor  the   Visual Studio debugger   or a debug message window        CrtDbgReport and  CrtDbgReportW create the user message for the debug report by substituting the argument n  arguments into the format   string  using the same rules defined by the printf or wprintf   functions  These functions then generate the debug report and   determine the destination or destinations  based on the current report   modes and file defined for reportType  When the report is sent to a   debug message window  the filename  lineNumber  and moduleName are   included in the information displayed in the window

User · Answer

If you want to print decimal variables   wchar t text buffer 20      0      temporary buffer swprintf text buffer   countof text buffer   L  d   your variable      convert OutputDebugString text buffer      print

User · Answer

Your Win32 project is likely a GUI project  not a console project  This causes a difference in the executable header  As a result  your GUI project will be responsible for opening its own window  That may be a console window  though  Call AllocConsole   to create it  and use the Win32 console functions to write to it

User · Answer

To print to the real console  you need to make it visible by using the linker flag  SUBSYSTEM CONSOLE  The extra console window is annoying  but for debugging purposes it s very valuable   OutputDebugString prints to the debugger output when running inside the debugger

User · Answer

You can also use WriteConsole method to print on console   AllocConsole    LPSTR lpBuff    Hello Win32 API   DWORD dwSize   0  WriteConsole GetStdHandle STD OUTPUT HANDLE   lpBuff  lstrlen lpBuff    amp dwSize  NULL

[c++] How do I print to the debug output window in a Win32 app?

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