Preprocessors: #if, #elif, #else, #endif

Preprocessors: #if, #elif, #else, #endif

Applies To: C++Builder 1 or higher
Category: C++ Language

The #if, #elif, #else and #endif are used to evaluate conditional statements. If the expression specified after #if is true, the compiler will execute the code between #if and #endif. You can also use #elif and #else to provide alternatives:

char *s;

#if 5 < 10

s = "5 is less than 10";

#else

s = "5 is greater than or equal to 10";

#endif

#if can be used with the defined preprocessor operator to check if an identifier was already defined using #define. The following example checks if VALUE is defined and if yes, it undefines it:

#define VALUE 100

#if defined VALUE

#undef VALUE

// Compiler error

int x = VALUE;