CODEWITHSUNDEEP
c++c-preprocessorstring-literals
Ian
Ian

Reputation: 4457

How to use Macro argument as string literal?

I am trying to figure out how to write a macro that will pass both a string literal representation of a variable name along with the variable itself into a function.

For example given the following function.

void do_something(string name, int val)
{
   cout << name << ": " << val << endl;
}

I would want to write a macro so I can do this:

int my_val = 5;
CALL_DO_SOMETHING(my_val);

Which would print out: my_val: 5

I tried doing the following:

#define CALL_DO_SOMETHING(VAR) do_something("VAR", VAR);

However, as you might guess, the VAR inside the quotes doesn't get replaced, but is just passed as the string literal "VAR". So I would like to know if there is a way to have the macro argument get turned into a string literal itself.

Upvotes: 117

Views: 199980

Answers (5)

Audrius Meškauskas
Audrius Meškauskas

Reputation: 21728

#define THE_LITERAL abcd

#define VALUE(string) #string
#define TO_LITERAL(string) VALUE(string)

std::string abcd = TO_LITERAL(THE_LITERAL); // generates abcd = "abcd"

Upvotes: 1

Zili
Zili

Reputation: 197

Perhaps you try this solution:

#define QUANTIDISCHI 6
#define QUDI(x) #x
#define QUdi(x) QUDI(x)
. . . 
. . .
unsigned char TheNumber[] = "QUANTIDISCHI = " QUdi(QUANTIDISCHI) "\n";

Upvotes: 15

Morwenn
Morwenn

Reputation: 22552

Use the preprocessor # operator:

#define CALL_DO_SOMETHING(VAR) do_something(#VAR, VAR);

Upvotes: 195

Mikele Shtembari
Mikele Shtembari

Reputation: 173

#define NAME(x) printf("Hello " #x);
main(){
    NAME(Ian)
}
//will print: Hello Ian

Upvotes: 15

Qaz
Qaz

Reputation: 61900

You want to use the stringizing operator:

#define STRING(s) #s

int main()
{
    const char * cstr = STRING(abc); //cstr == "abc"
}

Upvotes: 47

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