Help with const

I am working on a program in which I have the struct

Code:

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struct molecule {
        double x;
        double y;
        double z;
        double const radius = .05;
};

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When I compile with g++ without the pedantic flag everything works fine; however, if I use the pedantic flag I get the following error:

Code:

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poundcake.h:34: error: ISO C++ forbids initialization of member ‘radius’
poundcake.h:34: error: making ‘radius’ static
poundcake.h:34: error: ISO C++ forbids initialization of member constant ‘radius’ of non-integral type ‘const double’

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I have read that you can only use const with types int and enum. Why is this? I don't understand why it would be a bad idea to make a double const.

Also, is there any difference between writing

Code:

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const int x

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versus

Code:

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int const x

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Thanks in advance.

Quote:

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Originally Posted by waterborne

I have read that you can only use const with types int and enum. Why is this? I don't understand why it would be a bad idea to make a double const.

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Your information is either incorrect or misinterpreted. You are allowed to initialise static const integer members directly with their declaration in the class definition. For static const non-integer members, you should perform the initialisation elsewhere, e.g., in a source file. For non-static const members, of whatever type, you should perform the initialisation in a constructor (or by using an aggregate initialiser, like how you might initialise an array).

Quote:

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Originally Posted by waterborne

Also, is there any difference between writing

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There is no real difference.