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objective-cmathpi

What's the difference between "pi" and "M_PI" in objc

Including some math in my code I stumbled over the constant "PI". At least in my Xcode version 4.6 I could use either one. But what is the difference between pi and M_PI? The documentation is little bit tight on that topic.

Solution

  • pi is defined in the "CarbonCore.framework" headers as

    extern const double_t pi  __OSX_AVAILABLE_BUT_DEPRECATED(__MAC_10_0, __MAC_10_8, __IPHONE_NA, __IPHONE_NA);

    but marked as "deprecated". I assume that it is a relict from older Carbon frameworks.

    M_PI is defined as a macro

    #define M_PI   3.14159265358979323846264338327950288

    in math.h and part of the POSIX standard.

    The values are identical, but you should use M_PI for portability reasons.

    (And for Swift, see How to get mathemical PI constant in Swift)