FIX: IOMANIPdeclare Macro Causes C2758 Error with References

View products that this article applies to.

This article was previously published under Q148686

SYMPTOMS

When a IOMANIPdeclare() macro is used with a reference type, the compiler generates the following error message:

error C2758: '_tp' : must be initialized in constructor base/member initializer list

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The IOMANIPdeclare() macro is expanded into a number of classes containing data members of the type passed into the IOMANIPdeclare() macro. The constructors for these classes are written such that the data members are initialized in the body of each class constructor. This is not allowed for reference type data members. Reference type data members should be initialized in a member initialization list for the class constructor.

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RESOLUTION

Modify the IOMANIPdeclare() macro (defined in Iomanip.h) so that the class data members are initialized in a member initialization list instead of in the body of the constructor.

For example, the following line is defined in the IOMANIPdeclare() macro definition:

SMANIP(T)(ios& (*f)(ios&,T), T t) { _fp = f; _tp = t; }

The inline constructor body where the class data members are initialized can be modifed so that the constructor uses a member initialization list as follows:

SMANIP(T)(ios& (*f)(ios&,T), T t) : _fp(f), _tp(t) {}

This change must be made for each class constructor that initializes the _fp and _tp data members. These declarations are:

SMANIP(T)(ios&amp; (*f)(ios&amp;,T), T t) { _fp = f; _tp = t; }
IMANIP(T)(istream&amp; (*f)(istream&amp;,T), T t) { _fp = f; _tp = t; }
OMANIP(T)(ostream&amp; (*f)(ostream&amp;,T), T t) { _fp = f; _tp = t; }
IOMANIP(T)(iostream&amp; (*f)(iostream&amp;,T), T t) { _fp = f; _tp = t; }

After making this change, you can use reference data types in the IOMANIPdeclare() macro.

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STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

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MORE INFORMATION

Sample Code

/*
The following sample code demonstrates both the error, and the
workaround.

Compile options needed: none
                        /DWORKAROUND to enable the workaround macro
*/ 

#include <iostream.h>
#include <iomanip.h>

// --------------------------------------------------------
// following is the workaround macro

#ifdef WORKAROUND

#ifdef IOMANIPdeclare
#undef IOMANIPdeclare

#define IOMANIPdeclare(T)  \ 
class SMANIP(T) { \ 
public: \ 
  SMANIP(T)(ios& (*f)(ios&,T), T t) : _tp(t), _fp(f) {} \ 
  friend istream& operator>>(istream& s, const SMANIP(T) & sm) { \ 
    (*(sm._fp))(s,sm._tp); return s; \ 
  } \ 
  friend ostream& operator<<(ostream& s, const SMANIP(T) & sm) { \ 
    (*(sm._fp))(s,sm._tp); return s; \ 
  } \ 
private: \ 
  ios& (* _fp)(ios&,T); \ 
  T _tp; \ 
}; \ 
class SAPP(T) { \ 
public: \ 
  SAPP(T)( ios& (*f)(ios&,T)) { _fp = f; } \ 
  SMANIP(T) operator()(T t) { return SMANIP(T)(_fp,t); } \ 
private: \ 
  ios& (* _fp)(ios&,T); \ 
}; \ 
class IMANIP(T) { \ 
public: \ 
  IMANIP(T)(istream& (*f)(istream&,T), T t) : _tp(t), _fp(f) {} \ 
  friend istream& operator>>(istream& s, IMANIP(T) & sm) { \ 
    (*sm._fp)(s,sm._tp); return s; \ 
  } \ 
private: \ 
  istream& (* _fp)(istream&,T); \ 
  T _tp; \ 
}; \ 
class IAPP(T) { \ 
public: \ 
  IAPP(T)( istream& (*f)(istream&,T)) { _fp = f; } \ 
  IMANIP(T) operator()(T t) { return IMANIP(T)(_fp,t); } \ 
private: \ 
  istream& (* _fp)(istream&,T); \ 
}; \ 
class OMANIP(T) { \ 
public: \ 
  OMANIP(T)(ostream& (*f)(ostream&,T), T t) : _tp(t), _fp(f) {} \ 
  friend ostream& operator<<(ostream& s, OMANIP(T) & sm) { \ 
    (*sm._fp)(s,sm._tp); return s; \ 
  } \ 
private: \ 
  ostream& (* _fp)(ostream&,T); \ 
  T _tp; \ 
}; \ 
class OAPP(T) { \ 
public: \ 
  OAPP(T)(ostream& (*f)(ostream&,T)) { _fp = f; } \ 
  OMANIP(T) operator()(T t) { return OMANIP(T)(_fp,t); } \ 
private: \ 
  ostream& (* _fp)(ostream&,T); \ 
}; \ 
class IOMANIP(T) { \ 
public: \ 
  IOMANIP(T)(iostream& (*f)(iostream&,T), T t) : _tp(t), _fp(f) {} \ 
  friend istream& operator>>(iostream& s, IOMANIP(T) & sm) { \ 
    (*sm._fp)(s,sm._tp); return s; \ 
  } \ 
  friend ostream& operator<<(iostream& s, IOMANIP(T) & sm) { \ 
    (*sm._fp)(s,sm._tp); return s; \ 
  } \ 
private: \ 
  iostream& (* _fp)(iostream&,T); T _tp; \ 
}; \ 
class IOAPP(T) { \ 
public: \ 
  IOAPP(T)( iostream& (*f)(iostream&,T)) { _fp = f; } \ 
  IOMANIP(T) operator()(T t) { return IOMANIP(T)(_fp,t); } \ 
private: \ 
  iostream& (* _fp)(iostream&,T); \ 
};
#endif  //IOMANIPdeclare

#endif  //WORKAROUND

// This is the end of the workaround macro
// --------------------------------------------------------

typedef  int& fillpair;

IOMANIPdeclare( fillpair );

ostream& fp( ostream& os, fillpair pair ) {
  for ( int c = 0; c < 10; c++ ) {
    os << pair;
  }
  return os;
}

OMANIP(fillpair) fill( fillpair var ) {
  return OMANIP(fillpair)( fp, var);
}

void main() {
  int test=0;
  fillpair var=test;

  cout << "10 things coming " << fill( var ) << " done " << endl;
}
// ***** End of code sample ******

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