class A;

A g_a;

throw g_a;

const A g_a;

15.1.3
A throw-expression initializes a temporary object, called the exception object, the type of which is determined by removing
any top-level cv-qualifiers from the static type of the operand of throw and adjusting the type from “array of T”
or “function returning T” to “pointer to T” or “pointer to function returning T”, respectively. [ Note: the temporary object
created for a throw-expression that is a string literal is never of type char* or wchar_t*; that is, the special conversions
for string literals from the types “array of const char” and “array of const wchar_t” to the types “pointer to char”
and “pointer to wchar_t”, respectively (4.2), are never applied to a throw-expression. —end note ] The temporary is
an lvalue and is used to initialize the variable named in the matching handler (15.3). The type of the throw-expression
shall not be an incomplete type, or a pointer to an incomplete type other than (possibly cv-qualified) void. Except for
these restrictions and the restrictions on type matching mentioned in 15.3, the operand of throw is treated exactly as a
function argument in a call (5.2.2) or the operand of a return statement.

  throw exception_type("message");

  throw special_exception_type();

SEV>const A g_a;
SEV>

#include <iostream>

class A
{
public:
    A()         { std::cerr<< "c-tor " << this <<std::endl; }
    A(const A&) { std::cerr<< "copy c-tor " << this <<std::endl; }
    ~A()        { std::cerr<< "d-tor " << this <<std::endl; }
};

const A a;

int main(int argc, char *argv[])
{
    try
    {
        throw a;
    }
    catch(A& err)
    {
        std::cerr<<" At catch:\n"
                << "&a  = " << &a <<"\n"
                << "&err= " << &err << "\n";
    }

    return 0;
}

c-tor 00409158
copy c-tor 002DFF53
 At catch:
&a  = 00409158
&err= 002DFF53
d-tor 002DFF53
d-tor 00409158

SEV>throw g_a;
SEV>

throw &g_a;