Home / Questions / 77012
Accepted
simon
Asked: 2020-06-09 09:04:52 +0800 CST 2020-06-09 09:04:52 +0800 CST

What is the difference between macro and const in C?

  • 772

Going over C, I was wondering:

What is the difference between macros and consts, if in general the purpose of each one is to create a value that never changes?

Example of using a const:

#include <stdio.h>

void main()
{
    const int height = 100; /*constante de tipo entera*/
    const float number = 3.14; /*constante de tipo real*/
    const char letter = 'A'; /*constante de tipo caracter*/
    const char letter_sequence[10] = "ABC"; /*constante de tipo cadena*/
    const char backslash_char = '\?'; /*contante de caracter especial*/
    printf("Valor de la altura :%d \n", height );
    printf("valor del número : %f \n", number );
    printf("valor de la letra : %c \n", letter );
    printf("Valor de la secuencia de letras : %s \n", letter_sequence);
    printf("Valor del caracter de barra invertida : %c \n", backslash_char);
}

Example of the use of macros:

#include<stdio.h>
#define PI 3.1416//Macro
int main(){
    int  x = 10:
    suma = PI + x;

    printf("la suma es %.2f",suma);

    return 0;
}
c

1 Answers

  1. Best Answer

    Macros are directives handled by the preprocessor... a macro ends up generating legal C code, which is what the compiler will ultimately receive.

    That is, for the following example:

    #define NUMERO 5

int main()
{
  printf("%d",NUMERO);
}

    The compiler would get the following:

    int main()
{
  printf("%d",5);
}

    On the other hand, constants are variable elements that cannot see their value modified. That is, for the following example:

    int main()
{
  const int constante = 5;

  printf("%d",constante);
}

    The compiler will have to pass the value of constanteto the function printf. The two calls could only be similar if the compiler introduces some optimization that allows to eliminate this intermediate step.

    • 4