Compile Conditional Field Text For Free

#if checks for the value of the symbol, while #ifdef checks the existence of the symbol (regardless of its value). +1 for explicitly pointing out that defining something to zero will disable #if, but not #ifdef. If FOO defined non-zero than the compiler compiles.

You use four preprocessor directives to control conditional compilation: #if : Opens a conditional compilation, where code is compiled only if the specified symbol is defined. #elif : Closes the preceding conditional compilation and opens a new conditional compilation based on if the specified symbol is defined.

Use the #ifdef statement when you want to compile a section only if a specified expression has been defined with #define. Use #ifndef when you want to compile a section only if a specified expression has not been defined.

Conditional compilation can be performed using commands like #ifdef, #endif, #ifndef, #if, #else and #elif in a C Program. Example : Printing the AGE macro, if AGE macro is defined, else printing Not Defined and ending the conditional compilation block with an #endif directive.

Conditional compilation provides a way of including or omitting selected lines of source code depending on the values of literals specified by the DEFINE directive. In this way, you can create multiple variants of the same program without the need to maintain separate source streams.

Conditional compilation is the process of selecting which code to compile and which code to not compile similar to the #if / #else / #endif in C and C++. Any statement that is not compiled in still must be syntactically correct.

Conditional compilation provides a way of including or omitting selected lines of source code depending on the values of literals specified by the DEFINE directive. In this way, you can create multiple variants of the same program without the need to maintain separate source streams.