Microsoft KB Archive/148686

= FIX: IOMANIPdeclare Macro Causes C2758 Error with References =

Article ID: 148686

Article Last Modified on 12/2/2003

-

APPLIES TO


 * Microsoft Visual C++ 1.52 Professional Edition
 * Microsoft Visual C++ 2.2
 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 4.1 Subscription
 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 6.0 Standard Edition

-



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



CAUSE
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.



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& (*f)(ios&,T), T t) { _fp = f; _tp = t; } IMANIP(T)(istream& (*f)(istream&,T), T t) { _fp = f; _tp = t; } OMANIP(T)(ostream& (*f)(ostream&,T), T t) { _fp = f; _tp = t; } IOMANIP(T)(iostream& (*f)(iostream&,T), T t) { _fp = f; _tp = t; } After making this change, you can use reference data types in the IOMANIPdeclare macro.



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.



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

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


 * 1) include 
 * 2) include 

// // following is the workaround macro


 * 1) ifdef WORKAROUND


 * 1) ifdef IOMANIPdeclare
 * 2) undef IOMANIPdeclare

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); \ };
 * 1) define IOMANIPdeclare(T) \
 * 1) endif //IOMANIPdeclare


 * 1) 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 ******

Additional query words: kbVC400bug 1.50 1.51 1.52b 1.52c 8.00c 9.10 10.00 10.10 10.20 iostream io library

Keywords: kbbug kbfix kbnoupdate kbcpponly kbcompiler kbarttypeinf KB148686

-

[mailto:TECHNET@MICROSOFT.COM Send feedback to Microsoft]

© Microsoft Corporation. All rights reserved.