Question

I have tried to use this suggestion to do a static assert, but I do not get a compilation error if I use it within a method of a template.

The example follows :

#include <iostream>

#define STATIC_ASSERT(expr, msg)               \
{                                              \
    char STATIC_ASSERTION__##msg[(expr)?1:-1]; \
    (void)STATIC_ASSERTION__##msg[0];          \
}

template <typename T >
class A
{
public:
  int foo(const int k )
  {
    // does not work
    STATIC_ASSERT( k > 9, error_msg );
    return k+5;
  }
};

int bar(const int k )
{
  // works fine
  //STATIC_ASSERT( k > 9, error_msg );
  return k+5;
}

int main()
{
  A<int> a;
  const int v = 2;

  std::cout<<a.foo(v)<<std::endl;
  std::cout<<bar(v)<<std::endl;

  // works fine
  //STATIC_ASSERT( v > 9, error_msg );
}

I compiled it with g++ 4.7.2, with a warning that VLAs are not supported by c++ ISO :

g++ -Wall -g  -std=c++98 -Wextra -pedantic gvh.cpp

So, why the compilation doesn’t fail when the STATIC_ASSERT is used within the template method? Is there a way to make it fail?

NOTE : I need a c++98 (maybe even c++03) solution, if possible only with macros.

Answer 1

Prior to C++11 I would normally do:

typedef int static_assert_something[something ? 1 : -1];

You can also look at boost static assert. But it is too bloated for my liking. It is easy to make things bigger, it is hard to make them any better.