Struct Redefinition

Hi, does there happen to be a way to concatenate random or unique constants (such as __FILE__ and __LINE__) to form the name of a struct? So you're guaranteed unique struct's and no redefinition errors?

Code:

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#define CREATE_STRUCT() struct s##__LINE__ {}

int main()
{
    CREATE_STRUCT() s1;
    CREATE_STRUCT() s2; //redefinition error
}

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I just want to know if it's possible. Thanks :)

I imagine you can, but how would you refer to it again later on?

What problem are you trying to solve?

Quote:

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Originally Posted by Salem

What problem are you trying to solve?

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Macro to create a randomly defined struct which avoids the redefinition error shown above. I guess it would be essentially the exact same thing as an anonymous struct, except you can define a constructor.

Quote:

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Originally Posted by Salem

I imagine you can, but how would you refer to it again later on?

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I suppose you couldn't (it's not necessarily necessary however). That's partly why I'm not actually using this in any projects. I was just wondering if this sort of thing is possible (for the future).

Doesn't the error message mention the name of the struct? You can also probably let the compiler output preprocessed file (-E with GCC).

I'm not much of a macro user, but some experimentation showed that this might work (as I understand the middle macro is needed to get __LINE__ replaced with the number.

Code:

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#define CREATE_STRUCT() CREATE_STRUCT_IMP1(__LINE__)
#define CREATE_STRUCT_IMP1(id) CREATE_STRUCT_IMP2(id)
#define CREATE_STRUCT_IMP2(id) struct s##id {}

int main()
{
    CREATE_STRUCT() s1;
    CREATE_STRUCT() s2;
}

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It would be interesting to know indeed, what kind of problem this is supposed to solve.

You got it, nice job anon! Thanks guys!

Quote:

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Originally Posted by anon

It would be interesting to know indeed, what kind of problem this is supposed to solve.

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Originally it was intended to shorten my macro so that I wasn't forced to come up with my own struct names (one of the commonly recommended tips is to choose specific unique struct names when defining them locally), and could just have the macro randomly generate one. The reason not to use an anonymous struct would be because you cannot have a constructor, and I required one. Now the only problem with this is that you can't get the type of the class, like if you need to pass one of the struct's functions as a parameter (boost::bind/boost::function/etc.). Hence why I have no use for this at the moment, but I was interested to see if it was even possible considering the time I spent on it, and I feel knowing how to convert macro strings into definitions may come in handy in the future.

http://cboard.cprogramming.com/cplus...callbacks.html

Have you considered defining the struct in an anonymous namespace? This would be the appropriate approach if you want to define a helper struct in a source file to serve as implementation detail.