Question

Good day everybody!

Having the following code:

template<typename T, typename OutStream = std::ostream>
struct print
{
    OutStream &operator()(T const &toPrint, OutStream &outStream = std::cout) const
    {
        outStream << toPrint;
        return outStream;
    }
};

template<typename T, typename Index = unsigned int, typename CharType = char, typename OutStream = std::ostream>
struct print<T *, Index>
{
    print(CharType delimiter = ' '): delimiter_(delimiter) {}
    OutStream &operator()(T const *toPrint, Index startIndex, Index finishIndex, OutStream &outStream = std::cout) const
    {
        for (Index i(startIndex) ; i < finishIndex ; ++i)
            outStream << toPrint[i] << delimiter_;
        return outStream;
    }
protected:
    CharType delimiter_;
};

Compiler: MSVCPP10

Compiler Output:

1>main.cpp(31): error C2764: 'CharType' : template parameter not used or deducible in partial specialization 'print<T*,Index>'
1>main.cpp(31): error C2764: 'OutStream' : template parameter not used or deducible in partial specialization 'print<T*,Index>'
1>main.cpp(31): error C2756: 'print<T*,Index>' : default arguments not allowed on a partial specialization

I’m stuck. Help me to finish partial specialization.

Thanks!

Answer 1

I assume this is what you mean: (This may be incorrect code, I’m only trying to translate what you wrote)

template<typename T> struct print<T*, unsigned int> {
  typedef unsigned int Index;
  typedef std::ostream OutStream;
  typedef char CharType;
  print(CharType delimiter = ' '): delimiter_(delimiter) {}
  OutStream &operator()(T const *toPrint, Index startIndex, Index finishIndex, OutStream &outStream = std::cout) const {
    for (Index i(startIndex) ; i < finishIndex ; ++i)
      outStream << toPrint[i] << delimiter_;
    return outStream;
  }
protected:
  CharType delimiter_;
};

The compiler explains what went wrong:

default arguments not allowed on a partial specialization

Meaning things like typename Index = unsigned int can only appear in the non-specialized template.

template parameter not used or deducible in partial specialization

Meaning you must use all the parameters in this part: struct print<HERE>