Error: template argument uses local type

[Gabriel Schreiber]

Hi

this code:

#include <vector>
void f()
{
struct arg{};
std::vector<arg> v;
};

gets the error message:
: template-argument `f()::arg' uses local type `f()::arg'
: template argument 2 is invalid

can anyone explain this?

And: Is it possible in any way to instantiate templates with local
types?

TIA
Gabriel

 

[Rolf Magnus]

Hi

this code:

#include <vector>
void f()
{
struct arg{};
std::vector<arg> v;
};

gets the error message:
: template-argument `f()::arg' uses local type `f()::arg'
: template argument 2 is invalid

can anyone explain this?

The compiler already said it. You're using a local type as template
argument, and that's not allowed in c++. Put the struct definition
ouside the function, and it should work.

And: Is it possible in any way to instantiate templates with local
types?

No.

 

[tom_usenet]

Hi

this code:

#include <vector>
void f()
{
struct arg{};
std::vector<arg> v;
};

gets the error message:
: template-argument `f()::arg' uses local type `f()::arg'
: template argument 2 is invalid

can anyone explain this?

And: Is it possible in any way to instantiate templates with local
types?

No, the problem is that template arguments must have external linkage,
but local types have no linkage. You can move the struct to an
anonymous namespace to work around the problem without polluting a
namespace with your type.

You might want to read this:
http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1427.pdf

Tom

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