Why Can't Strings Be Used as Non-Type Template Parameters in C ?

Why Can't Non-Type Template Parameters Be Strings?

In C , non-type template parameters must be constant integral expressions. However, the code below attempts to use a std::string as a non-type template parameter:

template <std::string temp>
void foo()
{
     // ...
}

This results in a compiler error indicating that std::string is an illegal type for a non-type template parameter.

The reason for this restriction is that non-constant expressions cannot be parsed and substituted during compilation. They could change during runtime, which would require generating a new template at runtime. Since templates are a compile-time concept, this is not possible.

The C 11 standard explicitly allows only certain types for non-type template parameters:

• Integral or enumeration types
• Pointers to objects or functions
• Lvalue references to objects or functions
• Pointers to members
• std::nullptr_t

The above is the detailed content of Why Can't Strings Be Used as Non-Type Template Parameters in C ?. For more information, please follow other related articles on the PHP Chinese website!