Is there a way to prohibit the use of a class by value in c style variable arguments list?

Question

Accidential use of classes inside of c style typeless variable arguments list is a common error source. Example:

class MyString {
    public:
    char *pChars;
    int Length;

    MyString(char *pChars) {
        this->pChars = pChars; 
        Length = strlen(pChars); 
        } };

int main() {
    MyString s1("Bla1"), s2("Bla2");
    printf("%s%s", s1, s2); // This does not but should give a compiler warning/error!
    return 0; }

The printf call there receives the two s objects by value. that means all of their members are simply memory copied. But they are interpreted a simple char pointers. Result is a runtime error of course.

I am not asking for a solution to this, but I would like to have something I could add to my class so that the compiler warns me about it or gives an error.

Already tried to declarate but not implement a copy constructor. But it seems that no copy constructor is called. :-(

Please just answer to the question in the title. I do not need a discusson of why you should not use printf or these variable arguments lists - know that.

Thanks for your time.

Answer 1

Decent compilers (like gcc) check whether printf arguments match format specifiers in format string.

Just do not forget to add -Wformat or -Wall command line option.

http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Answer 2

Derive from boost::noncopyable

Answer 3

Hide copy constructor and assignment operator (declare them private, no need to implement them). Or derive the class from boost::noncopyable (which has the same effect).Passing arguments by value determines the usage of the copy constructor.