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Tip of the Day
Language: C++
Expertise: Intermediate
Mar 30, 2005

Restricting Implicit Conversion

The compiler performs implicit conversion whenever it feels the need for it. For example:

class test
   test (int y) : h(y)
       int h;

void func (test t)
    cout << t.h << '\n';

int main ()
        func (7);   //implcit conversion applied here
The previous code compiles successfully because the compiler implictly converts int to test by using its one-argument constructor.

To restrict this you can use the explicit keyword in the constructor, like this:

 explicit test (int y) : h(y)
Now, the program won't compile, and throws an error saying that int when it is expecting test.

If you still want to make it work, you can perform an explicit cast in the calling statement like this:

 func (static_cast<test>(7));
This way, there's no chance for the compiler to do anything backward.

Saurabh Ramya
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