C macro that concats two templated types

Asked Sep 23 '19 at 13:42

Active Sep 23 '19 at 14:05

Viewed 44 times

I my C++ project I would like to create a new type and automatically create a variable of the type. Suppose we have a 2 typename template struct my_struct

Now I am using

#define FOO(a,b) my_struct<a,b> var_ ## a ## b

which works fine when using POD types or simple structure names, like

FOO(int,double)
FOO(string,double)

But it doesn't work with C++ template types.

FOO(vector<int>,map<int,double>)

Is there any solution for it?

I wouldn't like to require a typedef workaround solution to use the macro

typedef my_vec = vector<int>

edited Sep 23 '19 at 14:05

asked Sep 23 '19 at 13:42

ztik

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What do you need this for? What's the use of `FOO(int,double)` == `intdouble`? – HolyBlackCat Sep 23 '19 at 13:44
`##` is for concatenation, `#` is for stringification. Your `FOO(vector,map)` yields `vectormap` – Alexander Dmitriev Sep 23 '19 at 13:46
Is there any way to drop `<>` using macros or other. I need to automatically create variable names in a more complicated implementation – ztik Sep 23 '19 at 13:48
@ztik If you need this to create variable names, maybe you could use variable templates instead? – HolyBlackCat Sep 23 '19 at 13:50
@HolyBlackCat I need to automatically give a name to the variable. The basic example `template constexpr T pi = T(3.1415926535897932385L);` has a user defined name `pi`. – ztik Sep 23 '19 at 13:55
@ztik Can you explain why you need it? In what way generating a variable name is better than using a template variable? – HolyBlackCat Sep 23 '19 at 13:59
It's still unclear. What stops you from using `template my_struct var;`? – HolyBlackCat Sep 23 '19 at 14:13

C macro that concats two templated types

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