Examples

Example 1: Overloading. Say you have a Widget::Widget( unsigned int ) that can be invoked implicitly, and a Display function overloaded for Widgets and doubles. Consider the following overload resolution surprise:

void Display( double );             // displays a double


void Display( const Widget& );      // displays a Widget





Display( 5 );                       // oops: creates and displays a Widget

Example 2: Errors that work. Say you provide operator const char* for a String class:

class String {


  // …


public:


  operator const char*();          // deplorable form


};

Suddenly, a lot of silly expressions now compile. Assume s1, s2 are Strings:

int x = s1 - s2;                // compiles; undefined behavior


const char* p = s1 - 5;         // compiles; undefined behavior


p = s1 + '0';                   // compiles; doesn't do what you'd expect


if( s1 == "0" ) { ...}          // compiles; doesn't do what you'd expect

The standard string wisely avoids an operator const char* for exactly this reason.