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Bug 5252

Summary: Build warning on MSVC: M_PI redefined
Product: SDL Reporter: Albert Vaca Cintora <albertvaka>
Component: buildAssignee: Sam Lantinga <slouken>
Status: ASSIGNED --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 Keywords: target-2.0.16
Version: 2.0.12   
Hardware: All   
OS: Windows 10   

Description Albert Vaca Cintora 2020-08-09 18:26:27 UTC 
On MSVC, including SDL.h and later including math.h, produces:

warning C4005: 'M_PI': macro redefinition

This is because SDL defines its own M_PI constant and math.h tries to define it again.

Instead of defining our own M_PI in SDL_stdinc.h, we should include math.h instead.

Note that, on top of that, MSVC needs _USE_MATH_DEFINES to be defined before including math.h, otherwise it won't define M_PI.
Comment 1 Albert Vaca Cintora 2020-08-10 23:22:19 UTC 
I found this problem is quite more easy to reproduce than I thought. If _USE_MATH_DEFINES is set, just by including SDL.h we trigger the compiler warning in MSVC about M_PI being redefined.

This is due to the following include chain:

SDL.h -> SDL_main.h -> SDL_stdinc.h -> #define M_PI
SDL.h -> SDL_thread.h -> process.h -> corecrt_startup.h -> math.h -> #define M_PI again (if _USE_MATH_DEFINES is set)

I think SDL should not define M_PI itself and instead include math.h
Comment 2 Albert Vaca Cintora 2020-08-23 16:35:52 UTC 
It seems this fork of SDL has a similar fix to what I'm proposing here, so at least one more person found this annoying: https://github.com/Jimbly/SDL/commit/2e42806dbca55a22b5b15a4a5becc779f2118735