Incrementing a pointer

[PaperPilot]

I have created a new data class which consists of four floats. I have created the copy constructor and the assignment operator= and they seem all right.

How do I define an operator++ for the pointer to the new data type?

Thanks in advance.

[horace1]

I have created a new data class which consists of four floats. I have created the copy constructor and the assignment operator= and they seem all right.

How do I define an operator++ for the pointer to the new data type?

Thanks in advance.

The problem with the increment and decrement operators is that there are prefix and postfix versions, i.e. ++i, i++, --i and i--. To differentiate between the prefix and postfix versions of operator++ and operator-- the compiler adds a dummy int parameter to the postfix call. e.g. from a class which processes octal number

        int operator++(void)                                        // prefix ++
            { 
             return octal_data = (octal_data + 1) % 8;     // increment & return
            }
        int operator++(int)                                        // postfix ++
            {                                                  
             int temp = octal_data;                        // save current value
             octal_data = (octal_data + 1) % 8;                     // increment
             return temp;                                    // return old value
            }
 

[PaperPilot]

What you say is true, horace1, but your example increments data, while I need to increment and decrement a pointer to that data. Like:

floatData[2] = { 5.9f, 4.8f };
*fltPtr = floatData;                // Pointer points to 5.9
++fltPtr;                           // increment pointer by 4 bytes
cout << *flpPtr;                    // Prints 4.8
 
 

I need to over ride the function: ++fltPtr

Thanks

[horace1]

What you say is true, horace1, but your example increments data, while I need to increment and decrement a pointer to that data. Like:

floatData[2] = { 5.9f, 4.8f };
*fltPtr = floatData;                // Pointer points to 5.9
++fltPtr;                           // increment pointer by 4 bytes
cout << *flpPtr;                    // Prints 4.8
 
 

I need to over ride the function: ++fltPtr

Thanks

no need as pointer arithmetic automatically takes account of the length of an object, e.g. as with structures in C

[PaperPilot]

no need as pointer arithmetic automatically takes account of the length of an object, e.g. as with structures in C

I have a class not a structure:

class  WindsTableElement
{
 
 public:
  float altitude;      ///< Current altitude in feet above sea level.
  float windMagnitude; ///< Wind velocity magnitude in ft/s.
  float windDirection; ///< Wind velocity direction in degrees with  
                        ///< respect to north.
  float windUpdraft;   ///< Wind updraft in ft/s.
 
WindsTableElement();
 
WindsTableElement(const WindsTableElement &); 
 
const WindsTableElement &operator=(const WindsTableElement &);
 
};
 

Do you mean if I have a pointer

WindsTableElement *wtePtr;

and I write

++wtePtr

that wtePtr will increment by 16?

If so, why does the compiler gvie me an error for not overloadng an operator++ for a pointer to WindsTableElement?

[horace1]

I have a class not a structure:
Do you mean if I have a pointer

WindsTableElement *wtePtr;

and I write

++wtePtr

that wtePtr will increment by 16?

If so, why does the compiler gvie me an error for not overloadng an operator++ for a pointer to WindsTableElement?

yes, consider the following

#include <iostream>
using namespace std;
 
class  WindsTableElement
{
 public:
  float altitude;      ///< Current altitude in feet above sea level.
  float windMagnitude; ///< Wind velocity magnitude in ft/s.
  float windDirection; ///< Wind velocity direction in degrees with  
                        ///< respect to north.
  float windUpdraft;   ///< Wind updraft in ft/s.
 
WindsTableElement() {};  // ** default constructor
 
WindsTableElement(const WindsTableElement &); 
 
const WindsTableElement &operator=(const WindsTableElement &);
 
};
 
int main()
{
    WindsTableElement x, w[10];
    WindsTableElement *ptr =w;
    for (int i=0; i<5;i++)
     cout << " ptr " << ptr++ << endl;  // ** this OK
    //x++;                                // ** cannot do this
    cin.get();
}
 

when run this prints

ptr 0x22fed0
ptr 0x22fee0
ptr 0x22fef0
ptr 0x22ff00
ptr 0x22ff10

on each loop the pointer is incremeneted by 0x10 (16 decimal)

if you remove the // from the front of

    //x++;                                // ** cannot do this
 

you then get a compiler error message such as
no `operator++(int)' declared for postfix `++'

indicating you need an overloaded postfix operator++() for class WindsTableElement

no idea why you get an error, post the code ?

[PaperPilot]

Now the problem has to do with a pointer in std::copy. Here is my code:

#include <vector>
#include <iterator> 
#include <iostream>
using std::cout;
using std::endl;
#include "WindDataReceiveBuffer.h"
#include "BufferServer.h"
 
int main()
{
    BufferServer bs;
 
    WindDataReceiveBuffer *wd =  WindDataReceiveBuffer
       ::Instance();
 
    const int FLT_ARY_SIZE = 12;
    float flt[FLT_ARY_SIZE] = {45.6f, 34.0f, 67.5f, 56.4f, 20.0f, 
        41.45f, 89.0f, 11.5f, 34.5f, 11.6f, 30.6f, 29.45f};
    char byte[1000];
    byte[0] = 'W';
    byte[1] = 0;
    byte[2] = 3;
    memcpy(byte+3, flt, FLT_ARY_SIZE * 4 *sizeof(float));
    std::ostream_iterator< float > OutIter(cout, " ");
    std::copy(flt, flt+(FLT_ARY_SIZE*4), OutIter );
    bs.setBufr(byte, *wd);
 
    WindTable wt_;
    wt_ = wd->getWindTable();
    cout << endl << "Contents of float vector: ";
    std::copy(wt_.begin(), wt_.end(), OutIter);
    return 0;
}

The error message points to:

std::copy(wt_.begin(), wt_.end(), OutIter);

[tavianator]

Do wt_.begin() and wt_.end() return iterators? If so, that should work.

[horace1]

as indicated by tavianator the code looks OK as per specification of copy() see
http://www.josuttis.com/libbook/algo/copy1.cpp.html

- what is the error message ?

[PaperPilot]

as indicated by tavianator the code looks OK as per specification of copy() see
http://www.josuttis.com/libbook/algo/copy1.cpp.html

- what is the error message ?

Here is the error mesage:

d:/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_algobase.h:247: error: no match for 'operator=' in '(&__result)->std::ostream_iterator<_Tp, _CharT, _Traits>::operator* [with _Tp = float, _CharT = char, _Traits = std::char_traits<char>]() = *__first'
d:/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stream_iterator.h:192: note: candidates are: std::ostream_iterator<_Tp, _CharT, _Traits>& std::ostream_iterator<_Tp, _CharT, _Traits>::operator=(const _Tp&) [with _Tp = float, _CharT = char, _Traits = std::char_traits<char>]
d:/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stream_iterator.h:154: note: std::ostream_iterator<float, char, std::char_traits<char> >& std::ostream_iterator<float, char, std::char_traits<char> >::operator=(const std::ostream_iterator<float, char, std::char_traits<char> >&)