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A dbg(…) macro for C++
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Latest commit 4fd78a3 Jul 16, 2019


Build Status Build status Try it online License: MIT

A macro for printf-style debugging fans.

Debuggers are great. But sometimes you just don't have the time and nerve to set up everything correctly and just want a quick way to inspect some values at runtime.

This projects provides a single header file with a dbg(…) macro that can be used in all circumstances where you would typically write printf("…", …) or std::cout << … << std::endl;, but with a few extras.


#include <vector>
#include <dbg.h>

// You can use "dbg(..)" in expressions:
int factorial(int n) {
  if (dbg(n <= 1)) {
    return dbg(1);
  } else {
    return dbg(n * factorial(n - 1));

int main() {
  std::string message = "hello";
  dbg(message);  // [example.cpp:15 (main)] message = "hello" (std::string)

  const int a = 2;
  const int b = dbg(3 * a) + 1;  // [example.cpp:18 (main)] 3 * a = 6 (int)

  std::vector<int> numbers{b, 13, 42};
  dbg(numbers);  // [example.cpp:21 (main)] numbers = {7, 13, 42} (size: 3) (std::vector<int>)

  dbg("this line is executed");  // [example.cpp:23 (main)] this line is executed


  return 0;

The code above produces this output (try it yourself):

dbg(…) macro output


  • Easy to read, colorized output (colors auto-disable when the output is not an interactive terminal)
  • Prints file name, line number, function name and the original expression
  • Adds type information for the printed-out value
  • Specialized pretty-printers for containers, pointers, string literals, enums, std::optional, etc.
  • Can be used inside expressions
  • The dbg.h header issues a compiler warning when included (so you don't forget to remove).
  • C++11 compatible


To make this actually usable, the dbg.h header should to be available from all kinds of different places and in all kinds of environments. The quick & dirty way is to actually copy the header file to /usr/include or to clone the repository and symlink dbg.h to /usr/include/dbg.h.

git clone
sudo ln -s $(readlink -f dbg-macro/dbg.h) /usr/include/dbg.h

Ideally, if this turns out to be a good idea, we would ship packages for various distributions so you don't have to make untracked changes to your filesystem.


  • Set the DBG_MACRO_DISABLE flag to disabled the dbg(…) macro (i.e. to make it a no-op).
  • Set the DBG_MACRO_NO_WARNING flag to disabled the "'dbg.h' header is included in your code base" warnings.


If you want dbg(…) to work for your custom datatype, you can simply overload operator<< for std::ostream&:

std::ostream& operator<<(std::ostream& out, const user_defined_type& v) {
  out << "";
  return out;

If you want to modify the type name that is printed by dbg(…), you can add a custom get_type_name overload:

// Customization point for type information
namespace dbg_macro {
    std::string get_type_name(type_tag<bool>) {
        return "truth value";


This project is inspired by Rusts dbg!(…) macro.

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