Using an int as a template parameter that is not known until run-time

Question

I am trying to use an integer as a template parameter for a class. Here is a sample of the code:

template< int array_qty > 
class sample_class {

    p         


        

Answer 1

For C++ 11, non-type template arguments are restricted to the following (§14.3.2/1):

A template-argument for a non-type, non-template template-parameter shall be one of:

• for a non-type template-parameter of integral or enumeration type, a converted constant expression (5.19) of the type of the template-parameter; or
  
• the name of a non-type template-parameter; or
  
• a constant expression (5.19) that designates the address of an object with static storage duration and external or internal linkage or a function with external or internal linkage, including function templates and function template-ids but excluding non-static class members, expressed (ignoring parentheses) as & id-expression, except that the & may be omitted if the name refers to a function or array and shall be omitted if the corresponding template-parameter is a reference; or
  
• a constant expression that evaluates to a null pointer value (4.10); or
  
• a constant expression that evaluates to a null member pointer value (4.11); or
  
• a pointer to member expressed as described in 5.3.1.

In C++ 98 and 03, the list is even more restricted. Bottom line: what you're trying to do simply isn't allowed.