Macro constants

This post describes macro constants.

First, let’s briefly describe the preprocessor. The preprocessor runs before the program is compiled and processes preprocessor directives that begin with #. Examples include #define and others.

#define is a command that replaces a string (name) with a constant value. Constants defined using this command are called “macro constants.”

For example, if you define it as follows:

#define MAX_USERS 100

After this, if you write MAX_USERS in the program, the preprocessor will replace it with 100. This makes the code easier to understand and allows you to manage the value in one place.

Next, I will describe the purpose of using macro constants.

Improved readability

This is used to make the meaning of constants easier to understand.

#define iPI  3.14159

double area = iPI * r * r;

Improved maintainability

If the same value is used in multiple places, you only need to change the definition.

#define iBUFF_SIZE  128
unsigned char BUFF[iBUFF_SIZE]

    for( i=0 ; i<iBUFF_SIZE ; i++ )
    {
            sum = sum + BUFF[i]:

Elimination of unclear numerical values

If the meaning of the numerical values is unclear, use macro constants with labels to make the meaning easier to understand.

#define iSECOND_IN_A_DAY  60 * 60 *24 /* 86400s/Day */

  if( s < iSECOND_IN_A_DAY )
  {

Conditional compilation specifications

Used when switching program code with conditional compilation.

#define iTEST  1                 /* Debug SW 0:OFF 1:ON */

#ifdef iTEST == 1
    printf( "integer: %d", x);　/* Debug Code */
#endif