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Stringify Operators

Stringify operator #

The # operator is used to convert a macro argument into a string literal. This means that if you pass any value to the macro, it will be converted to a string.

Here is an example of usage:

main.c


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#include <stdio.h>
#define SQR(x) printf("Square " #x " = %d\n", ((x)*(x))) 

int main()
{
   int j = 5;
   SQR(j);
   return 0;
}

The #x operator in the SQR macro is used to turn the x argument into a string. When you pass the j variable to the macro, #x produces the string "j" (i.e. the variable name), not its value.

Thus, in the line

printf("Square " #x " = %d\n", )(x)*(x)));

#x causes the variable name to be included in the output, and x passes its value (in this case, 5).

If you use a number as an argument, #x will turn the number into a string and then treat it as a number:

main.c


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#include <stdio.h>
#define SQR(x) printf("Square " #x " = %d\n", ((x)*(x))) 

int main()
{
   int j = 5;
   SQR(j);
   SQR (54); // number as argument
   return 0;
}

Token Pasting operator ##

The ## operation combines two tokens into one.

main.c


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#include <stdio.h>
#define CONCAT(x, y) x##y

int main() {
    int myVariable = 10;                   // variable named `myVariable`
    printf("%d\n", CONCAT(my, Variable));  // Result: 10
    return 0;
}

The CONCAT(x, y) macro concatenates the tokens my and Variable, which results in the name myVariable - just like a variable name.

When you call CONCAT(x, y), the preprocessor replaces it with myVariable, and you can access the value of myVariable.

Opgave

Swipe to start coding

Complete the CREATE_VAR macro, which will concatenate the tokens token1 and token2;
Use the created macro to create the variable "myVariable";
Specify the name of the variable whose contents you want to display on the screen.

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Stringify Operators