Changing a macro at runtime in C

Question

I have a macro defined. But I need to change this value at run time depending on a condition. How can I implement this?

Answer 1

You can't.

As a macro is resolved by the preprocessor before the compilation itself, its content is directly copied where you use it.

You can still use parameters to insert a conditional statement depending on what you want, or use a call-scope accessible variable.

If you want to change a single value, better use global scope variable, even if such behavior is discouraged. (as the intensive use of macro)