C++ how can i use the same .h and choose different .cpp when using the same .h？

Question

这里的场景是：“baselogger.h”包含API，我在两种情况下实现这些API（case A和case B，A对应1.cpp，B对应2.cpp），那么如何编写宏来编译不同的使用不同的 cpp 在“baselogger.h”中实现 API 的情况？

Answer 1

You don't necessarily need a macro for this. You could instead compile and link with 1.cpp in case A and compile and link with 2.cpp in case B.

CMake example:

option (CASE_A "Descriptive description" ON)
if (CASE_A)
    target_sources(target_name PRIVATE 1.cpp)
else ()
    target_sources(target_name PRIVATE 2.cpp)
endif ()

Insted of option, you can have some other condition. This is often useful for porting API to different systems.

---

But a macro based solution works too:

// 1.cpp
#ifdef MACRO_CASE_A
// case A implementation for baselogger.h
#endif

// 2.cpp
#ifndef MACRO_CASE_A
// case B implementation for baselogger.h
#endif

In this approach, simply compile both sources always.