Using a integer for OutputDebugString in VS2017

Question

I've been searching around on the web for a while on how to output a integer or optionally a float using OutputDebugString(). It would be easier if i could write my debug data straight to the console from my external executable using this command. However i only got it to work with a const char. The solutions i found were outdated i tried copy and pasting the code straight from the web but didn't work. Even after modifying the code i couldn't get it to typecast correctly. Is there anyone that could help me typecast something into the OutputDebugString as clean as possible, it's for debugging purposes only so i rather keep the code short and easily readable than having a more complex and clunky typecast IF that is possible. Many thanks!

score 2 · Answer 1 · answered Aug 19 '19 at 07:06

Provided alternatively solution. The function below encapsulates OutputDebugString that can accept formatted arguments.

#include <vector>
#include <string>    
void DbgMsg(const char * zcFormat, ...)
{
    // initialize use of the variable argument array
    va_list vaArgs;
    va_start(vaArgs, zcFormat);

    // reliably acquire the size
    // from a copy of the variable argument array
    // and a functionally reliable call to mock the formatting
    va_list vaArgsCopy;
    va_copy(vaArgsCopy, vaArgs);
    const int iLen = std::vsnprintf(NULL, 0, zcFormat, vaArgsCopy);
    va_end(vaArgsCopy);

    // return a formatted string without risking memory mismanagement
    // and without assuming any compiler or platform specific behavior
    std::vector<char> zc(iLen + 1);
    std::vsnprintf(zc.data(), zc.size(), zcFormat, vaArgs);
    va_end(vaArgs);
    std::string strText(zc.data(), iLen);

    OutputDebugStringA(strText.c_str());
}

For example, the code below shows how to print an integer variable by OutputDebugString through DbgMsg().

int foo=12;
DbgMsg(" foo=%d", foo);

vsnprintf expects you to use C++11, any alternative (except sprintf) which could be used? — Thomas Piekarski, Mar 09 '22 at 16:29

score 1 · Answer 2 · answered Mar 25 '18 at 02:48

OutputDebugString can only take strings, if you want formatted output you will have to do that yourself before feeding it to OutputDebugString. If you are using MSVC I suggest that you use _CrtDbgReport or _CrtDbgReportW. With recent versions of MSVC that support variadic macros I use the following:

#if !defined(_RPTW)
#if defined(_DEBUG)
#define _RPTW(pszFmt, ...) _CrtDbgReportW(_CRT_WARN, NULL, __LINE__, NULL, (pszFmt), __VA_ARGS__)
#define _RPTW_(dest, fmt, ...) _CrtDbgReportW((dest), NULL, __LINE__, NULL, (pszFmt), __VA_ARGS__)
#else
#define _RPTW(pszFmt, ...)
#define _RPTW(dest, pszFmt)
#endif
#endif // #if !defined(_RPTW)

#if !defined(_RPTA)
#if defined(_DEBUG)
#define _RPTA(pszFmt, ...) _CrtDbgReport(_CRT_WARN, NULL, __LINE__, NULL, (pszFmt), __VA_ARGS__)
#define _RPTA_(dest, fmt, ...) _CrtDbgReport((dest), NULL, __LINE__, NULL, (pszFmt), __VA_ARGS__)
#else
#define _RPTA(pszFmt, ...)
#define _RPTA_(dest, pszFmt)
#endif
#endif // #if !defined(_RPTA)

#if !defined(_RPTT)
#if defined(_UNICODE)
#define _RPTT _RPTW
#define _RPTT_ _RPTW_
#else
#define _RPTT _RPTA
#define _RPTT_ _RPTA_
#endif
#endif // #if !defined(_RPTT)

The second forms allow providing a different level of report (_CRT_ASSERT or c_CRT_ERROR instead of _CRT_WARN)

@StackingLua, Since this issue has been resolved,would you please mark it as the answer? So it could help other community members who get the same issue. — Jack Zhai, Apr 03 '18 at 05:32

score 0 · Answer 3 · answered Mar 09 '22 at 16:25

I would recommend to use sprintf like that:

// issues with the int x, let's output and look at it in DebugView
char msg[255] = {0};
sprintf(msg, ">> Watch out x=%d\n", x);
OutputDebugString(msg);

Maybe I did not understand the question, but that's how I quickly dump integers. And to be honest I do not know these MACROS which SoronelHaetir listed but indeed you've got to format yourself. So I Hope this helps and is rather straight forward.

Using a integer for OutputDebugString in VS2017

3 Answers3