c++ - 编译器生成的错误方法调用

Question

window 7Cygwin 1.7.20海合会 4.5.3

我的一个类中有一个方法，enqueue(const PTR X, const void* operation)，当尝试调用它时，实际上调用了另一个方法，enqueue(bool X)' 当原始方法改为，enqueue(const PTR X) 调用正确。我无法弄清楚我可能做了什么来激起这种行为。代码是可编译的。

/****** SlipDef.h ******/

#ifndef SLIPDEF_H
#define SLIPDEF_H
# include <string>
# include "SlipPointer.h"
using namespace std;
namespace slip {
    typedef unsigned char   UCHAR;
    typedef signed   char   CHAR;
    typedef unsigned short  USHORT;
    typedef signed   short  SHORT;
    typedef unsigned int    UINT;
    typedef signed   int    INT;
    typedef unsigned long   ULONG;
    typedef signed   long   LONG;
    typedef float           FLOAT;
    typedef double          DOUBLE;
    typedef SlipPointer *   PTR;
    typedef SlipPointer *   STRING;
} // namespace slip
#endif  /* SLIPDEF_H */
/****** SlipHeader.h ******/

#ifndef _SLIPHEADER_H
#define _SLIPHEADER_H
# include <string>
# include "SlipDef.h"
namespace slip {

   class SlipHeader {
   public:
      SlipHeader&       enqueue(SlipHeader& X);
      SlipHeader&       enqueue(bool X);
      SlipHeader&       enqueue(UCHAR X);
      SlipHeader&       enqueue(CHAR X);
      SlipHeader&       enqueue(ULONG X);
      SlipHeader&       enqueue(LONG X);
      SlipHeader&       enqueue(DOUBLE X);
      SlipHeader&       enqueue(const PTR X, const void* operation);
      SlipHeader&       enqueue(const string& X, bool constFlag = false);
      SlipHeader&       enqueue(const string* X, bool constFlag = false);
    };
};
#endif  /* SLIPHEADER_H */

/****** SlipPointer.h ******/

#ifndef SLIPPOINTER_H
#define SLIPPOINTER_H
using namespace std;
namespace slip {

   class SlipPointer { 
   public:
   };
} // namespace slip
#endif  /* SLIPPOINTER_H */

/****** TheOtherHeader.h ******/

#ifndef _THEOTHERHEADER_H
#define _THEOTHERHEADER_H
# include <string>
# include "SlipDef.h"
namespace slip {

   class TheOtherHeader {
   public:
      TheOtherHeader&   enqueue(TheOtherHeader& X);
      TheOtherHeader&   enqueue(bool X);
      TheOtherHeader&   enqueue(UCHAR X);
      TheOtherHeader&   enqueue(CHAR X);
      TheOtherHeader&   enqueue(ULONG X);
      TheOtherHeader&   enqueue(LONG X);
      TheOtherHeader&   enqueue(DOUBLE X);
      TheOtherHeader&   enqueue(const PTR X);
      TheOtherHeader&   enqueue(const string& X, bool constFlag = false);
      TheOtherHeader&   enqueue(const string* X, bool constFlag = false);
    };
};
#endif  /* _THEOTHERHEADER_H */

/****** main.cpp ******/

# include "SlipHeader.h"
#include "TheOtherHeader.h"
# include <string>
# include <iostream>
using namespace std;
using namespace slip;

int main(int argc, char** argv) {
   SlipPointer*    ptr    = new SlipPointer();
   SlipHeader*     header = new SlipHeader();
   TheOtherHeader* theOtherHeader = new TheOtherHeader();
   header->enqueue(ptr);
   theOtherHeader->enqueue(ptr);
return 0;
}

/****** SlipHeader.cpp ******/

# include <string>
# include <iostream>
# include "SlipDef.h"
# include "SlipHeader.h"
namespace slip {
   static void* ptrOP;
   SlipHeader& SlipHeader::enqueue(SlipHeader& X) { cout << "enqueue(SlipHeader& X) wrong answer" << endl; return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(bool X)      { cout << "enqueue(bool X) wrong answer" << endl;      return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(UCHAR X)     { cout << "enqueue(UCHAR X) wrong answer" << endl;     return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(CHAR X)      { cout << "enqueue(CHAR X) wrong answer" << endl;      return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(ULONG X)     { cout << "enqueue(ULONG X) wrong answer" << endl;     return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(LONG X)      { cout << "enqueue(LONG X) wrong answer" << endl;      return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(DOUBLE X)    { cout << "enqueue(DOUBLE X) wrong answer" << endl;    return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(const PTR X, const void* operation = ptrOP) {
      cout << "enqueue(PTR X) right answer" << endl; return *new SlipHeader();
   };
   SlipHeader& SlipHeader::enqueue(const string& X, bool constFlag) { cout << "enqueue(string& X) wrong answer" << endl; return *new SlipHeader();}
   SlipHeader& SlipHeader::enqueue(const string* X, bool constFlag) { cout << "enqueue(string* X) wrong answer" << endl; return *new SlipHeader();}
};
/****** TheOtherHeader.cpp ******/

# include <string>
# include <iostream>
# include "SlipDef.h"
# include "TheOtherHeader.h"
namespace slip {
   static void* ptrOP;
   TheOtherHeader& TheOtherHeader::enqueue(TheOtherHeader& X) { cout << "enqueue(TheOtherHeader& X) wrong answer" << endl; return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(bool X)      { cout << "enqueue(bool X) wrong answer" << endl;      return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(UCHAR X)     { cout << "enqueue(UCHAR X) wrong answer" << endl;     return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(CHAR X)      { cout << "enqueue(CHAR X) wrong answer" << endl;      return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(ULONG X)     { cout << "enqueue(ULONG X) wrong answer" << endl;     return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(LONG X)      { cout << "enqueue(LONG X) wrong answer" << endl;      return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(DOUBLE X)    { cout << "enqueue(DOUBLE X) wrong answer" << endl;    return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(const PTR X) {
      cout << "enqueue(PTR X) right answer" << endl; return *new TheOtherHeader();
   };
   TheOtherHeader& TheOtherHeader::enqueue(const string& X, bool constFlag) { cout << "enqueue(string& X) wrong answer" << endl; return *new TheOtherHeader();}
   TheOtherHeader& TheOtherHeader::enqueue(const string* X, bool constFlag) { cout << "enqueue(string* X) wrong answer" << endl; return *new TheOtherHeader();}
};

Answer 1

const void* operation 有默认参数。但是，您在实现中而不是 header 中设置这些默认参数 - 应该是相反的方式:

// header
void f(int x=5);

// implementation
void f(int x) { }

原因很简单，如果在主代码中调用header->enqueue(ptr)，编译器只知道header给出的信息。如果 header 不包含默认参数，则编译器此时不知道默认参数的存在。