c++ - pointers to object with external linkage to Nontype template parameters -

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i tried following code.

template <int val> void printval() {     for(int i=0;i<val; i++){         cout << " value "<<i<<endl;     } }

instantiation: printval<100>()

when use (std::string s ) non type template parameter, compiler shouted @ me following error

"class std::basic_str<char>' not valid type template non-type parameter.

what know should use constant integral values only. not double.

question:

1) why should not use std::string, bothers ?

2) meaning of 'pointers objects external linkage can used'. can sample code it?

according 14.1/4,

a non-type template-parameter shall have 1 of following (optionally cv-qualified) types:

  • integral or enumeration type,
  • pointer object or pointer function,
  • lvalue reference object or lvalue reference function,
  • pointer member,
  • std::nullptr_t.

your std::string none of those.


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