CODEWITHSUNDEEP
c++macrosconsole-application
Abruzzo Forte e Gentile
Abruzzo Forte e Gentile

Reputation: 14869

print variable name in a #define

I am trying to print out to console using a macro the variable name for display members value while debugging ( logging ). How to do that? I tried the following but it doesnt' work.

#define MY_PRINT(x) std::cout << "'x'=" << x << std::endl;

int main(){
   int my_variable=3;
   MY_PRINT( my_variable );
   // I would like to print to console
   // 'my_variable'=3
}

Upvotes: 11

Views: 13289

Answers (2)

shodanho
shodanho

Reputation: 51

For C++ I use this:

#define STR(x) #x << '=' << x

int main()
{
  int i = 1;
  std::string str("hello");
  std::vector<std::string> vec;
  my_class mc;

  ...

  std::cout << STR(i) << std::endl
            << STR(str) << std::endl
            << STR(vec) << std::endl
            << STR(mc) << std::endl;

  return 0;
}

This way the compiler chooses the streaming operator based on the data type, so you don't need to bother with different macros for each, and it can go to any std::ostream, not just std::cout. Just provide the appropriate streaming operator for your data:

std::ostream operator<<(std::ostream&, const T&);
std::ostream operator<<(std::ostream&, const std::vector<T>&);
etc

But I wish there was a template way to replace the macro, or at least the variable name provided by the #x.

Upvotes: 5

Abruzzo Forte e Gentile
Abruzzo Forte e Gentile

Reputation: 14869

Auch... I found the solution.

I should write the macro like this

 #define MY_PRINT(x) std::cout << #x"=" << x << std::endl

Upvotes: 26

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