studoot / dbg-macro

A dbg(…) macro for C++

dbg(…)

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.

Examples

#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

  factorial(4);

  return 0;
}

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

Features

• 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

Installation

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 https://github.com/sharkdp/dbg-macro
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.

Customization

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";
    }
}

Acknowledgement

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