Question

I have a templated SortedLinkedList class that sorts Topic A objects by the value contained in their string field.

Here’s Topic A:

struct TopicA
{
string sValue;
double dValue;
int iValue; 

TopicA();
TopicA( const string & arg );

bool operator> ( const TopicA & rhs ) const;
bool operator< ( const TopicA & rhs ) const;
bool operator== ( const TopicA & rhs ) const;
bool operator!= ( const TopicA & rhs ) const;
};

I want to find the position in the list where a TopicA object with "tulgey" in its string field would be stored, so I call AList.getPosition( "tulgey" ); Here is the getPosition() header:

template <class ItemType>
int SortedLinkedList<ItemType>::getPosition( const ItemType& anEntry ) const

But when I try to call getPosition() the compiler gives me the error in the title. Why? Don’t I have a conversion constructor from string to TopicA?

If it makes any difference here’s the definition of TopicA( const string & arg ):

TopicA::TopicA( const string & arg ) : sValue( arg ), dValue( 0 ), iValue( 0 )
{
}

Answer 1

You are probably invoking two implicit conversions, from const char[7] to std::string, and from std::string to TopicA. But you are only allowed one implicit conversion. You can fix the problem by being more explicit:

AList.getPosition( std::string("tulgey") ); // 1 conversion
AList.getPosition( TopicA("tulgey") );      // 1 conversion

Alternatively, you can give TopicA a constructor taking a const char*:

TopicA( const char * arg ) : sValue( arg ), dValue( 0 ), iValue( 0 ) {}