CODEWITHSUNDEEP
c++
Johan
Johan

Reputation: 3819

C++ const string non template parameter

In C++ the following is legal:

template <int i>
run(){...}

run<3>(); // legal

const int j=3;
run<j>(); // legal because j is const

why the following are or aren't legal?

template <String s>
run(){...}

run<"hello">(); // legal or illegal?

const string s="hello";
run<s>(); // legal or illegal?

Upvotes: 0

Views: 79

Answers (2)

R Sahu
R Sahu

Reputation: 206617

From the C++11 Standard:

14.1 Template parameters

...

4 A non-type template-parameter shall have one of the following (optionally cv-qualified) types:
— integral or enumeration type,
— pointer to object or pointer to function,
— lvalue reference to object or lvalue reference to function,
— pointer to member,
— std::nullptr_t.

Hence, you cannot use a class as a non-type template parameter.

Upvotes: 6

Logicrat
Logicrat

Reputation: 4468

The int one is legal because the compiler knows about int. On the other hand, String is not a built-in C++ data type. It is defined in a header and library. The constant "hello" is an array of characters, not a String().

Upvotes: 1

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