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C++ Macros
Macros are preprocessing directives in C++ used by the preprocessor to perform text substitution. They are defined using the #define directive, followed by the macro name and the value to be substituted.
Macros can be used to define constants, create function-like macros, or perform conditional compilation.
Constant Macros
Constant macros are used to define symbolic constants for use in code. They do not use any memory and are replaced by the preprocessor before the compilation process.
Example:
#define PI 3.14159
This macro defines a symbolic constant PI. You can use it in your code as if it were a regular variable.
double circumference = 2 * PI * radius;
Function-like Macros
Function-like macros are similar to regular functions. They take a list of arguments and perform text substitution.
Example:
#define SQUARE(x) ((x) * (x))
This macro defines a function-like macro SQUARE that calculates the square of a number.
int square_of_five = SQUARE(5); // expands to ((5) * (5))
Conditional Compilation
Macros can be used for conditional compilation using the #ifdef, #ifndef, #if, #else, #elif, and #endif directives.
Example:
#define DEBUG_MODE
#ifdef DEBUG_MODE
// Code to be compiled only in debug mode
#else
// Code to be compiled only if DEBUG_MODE is not defined
#endif
This example demonstrates how you can use macros to control the parts of code that are being compiled, depending on the presence or absence of a macro definition.