Suppose I have a following code:
int main() {
#ifdef NEWMETHOD
val = new_method("hello world!");
#else
val = old_method("hello world!");
#endif
return 0;
}
How can I define NEWMETHOD during compile time?
You just need to write
#define NEWMETHOD
before you do the #ifdef
check.
Of course, then you wouldn't need to write the #ifdef
in the first place.
If you want to define the macro without changing the source code, you can pass it in during compilation with the -D
flag, like this:
g++ -DNEWMETHOD main.cpp
Obviously, replace the specific compiler command, and file name.
You can either
Define it by inserting
#define NEWMETHOD
into the source code before using it or
Add -DNEWMETHOD
to your compiler call (works with all popular compilers including GCC, clang and MSVC).
Depending on your build system you might want to add that to the CFLAGS
(C) or CXXFLAGS
(C++) environment variables.
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