Q148686: FIX: IOMANIPdeclare Macro Causes C2758 Error with References
Article: Q148686
Product(s): Microsoft C Compiler
Version(s): 1.52,2.2,4.0,4.1,4.2,5.0,6.0
Operating System(s):
Keyword(s): kbCompiler kbCPPonly kbGenInfo kbVC152bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug k
Last Modified: 11-FEB-2002
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The information in this article applies to:
- Microsoft Visual C++, versions 1.52, 2.2, 4.0, 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
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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.
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 ******
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 : kbCompiler kbCPPonly kbGenInfo kbVC152bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug kbNoUpdate kbArtTypeINF
Technology : kbVCsearch kbVC400 kbAudDeveloper kbVC220 kbVC410 kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVC152 kbVC500Search
Version : :1.52,2.2,4.0,4.1,4.2,5.0,6.0
Issue type : kbbug
Solution Type : kbfix
=============================================================================
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