How do you include a header file that may or may not exist?
c, gcc, header-files, include
Solution
In general, you'll need to do something external to do this - e.g. by doing something like playing around with the search path (as suggested in the comments) and providing an empty `foo.h` as a fallback, or wrapping the `#include` inside a `#ifdef HAS_FOO_H`...`#endif` and setting `HAS_FOO_H` by a compiler switch (`-DHAS_FOO_H` for gcc/clang etc.).
If you know that you are using a particular compiler, and portability is not an issue, note that some compilers do support including a file which may or may not exist, as an extension. For example, see clang's `__has_include` feature.
Problem
Let's assume I define BAR in foo.h. But foo.h might not exist. How do I include it, without the compiler complaining at me? ``` #include "foo.h" #ifndef BAR #define BAR 1 #endif int main() { return BAR; } ``` Therefore, if BAR was defined as 2 in foo.h, then the program would return 2 if foo.h exists and 1 if foo.h does not exist.