copysign undefined

This is a discussion on copysign undefined within the Windows Programming forums, part of the Platform Specific Boards category; I want to use the function (double) copysign from math.h but I get the following warning: warning C4013: 'copysign' undefined; ...

  1. #1
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    copysign undefined

    I want to use the function (double) copysign from math.h but I get the following warning:
    warning C4013: 'copysign' undefined; assuming extern returning int
    I have used #include <math.h> so I do not understand how this function can not be defined. Furthermore, in Tools-> Options -> Projects and Solutions -> VC++ Directories I have $(VCInstallDir)include in my Include files and $(VCInstallDir)lib in my Library files. What else do I need to do?

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    There is no function named copysign. There is, however, a function named _copysign (not the underscore).
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    ok, I clearly didn't pay attention. Thanx.

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