error: cannot increment value of type 'char [6]'

I am trying to learn pointers and string literals in C/C++. As per my understanding, string literals are char arrays with a null \0 at the end. Also we can basically do all the pointer arithmetic operations on array like increment and decrement.

But when I am trying to run the following code:

#include <iostream> 
using namespace std;

int main (){
    char *c ="Hello";
    char d[6];

    while(*d++ = *c++);

    cout<<c<<endl<<d;
} 

I am getting the following error,

error: cannot increment value of type 'char [6]'
    while(*d++ = *c++);

My assumption for this code was, that the values of string literal c will be copied to char array d.

convert mat to ipl image in opencv 3.0

I tried to convert mat image to IplImage but i could not able to convert it , i tried like this

Mat frame=imread("image path");
IplImage* image=IplImage(frame);

I got the error like cannot convert 'IplImage {aka _IplImage}' to 'IplImage* {aka _IplImage*}' in initialization...please any one tell how to convert in opencv 3.0

implementing matlab hist() in c++

here is the line of code I want to implement

kb = [];
    for k = 1:length(nRef)
        for n=1:length(dCmpInd{k})
            x = [centroid(nRef{k}, 1), centroid(dCmpInd{k}(n),1)];
            y = [centroid(nRef{k}, 2), centroid(dCmpInd{k}(n),2)];

            [x,ind] = sort(x);
            y = y(ind);
            kb = [kb diff(y) / diff(x)];
        end
    end

    theta = (atan(kb));

    [N, X] = hist(abs(theta),2);

here is my c++ code:

 std::vector<double> kb;
    std::vector<double> theta;
    for (int k = 0; k < nRef.size(); k++)
    {
        for (int n = 0; n < dCmpInd[k].size(); n++)
        {
            double x1 = centroids[nRef[k]].m_X; double x2 = centroids[dCmpInd[k][n]].m_X;
            double y1 = centroids[nRef[k]].m_Y; double y2 = centroids[dCmpInd[k][n]].m_Y;
            if (x1 <x2)
            {
                double tempdiff = (y2-y1)/(x2-x1);              
                kb.push_back(tempdiff);
                theta.push_back(abs(atan(tempdiff)));
            }
            else
            {
                double tempdiff = (y1-y2)/(x1-x2);
                kb.push_back(tempdiff);
                theta.push_back(abs(atan(tempdiff)));
            }
        }
    }

is there a quick way to implement :

[N,X] = hist(theta,2);

I can use openCV 2.4.10 as well but calcHist() isn't really the same, I need to create 2 bins.

my input is 1D array:

0.00598881028540019 1.56120677124307    0.00598881028540019 0.00669537049433832 1.37723800334516    1.37723800334516    1.36424594043624    1.56120677124307    0.0152220988707370

the output is:

X= 0.394793300524817    1.17240228100365
 N = 4 5

C++ this pointer equivalent in Python ctypes

I'm calling a C dll from Python using ctypes and having some trouble passing the correct parameters to the IBSU_RegisterCallbacks function, defined below.

int WINAPI IBSU_RegisterCallbacks
    (const int         handle, 
     const IBSU_Events event, 
     void             *pCallbackFunction,
     void             *pContext);

It describes the final parameter as:

/* pContext Pointer to user context that will be passed to callback function.*/

A working C++ example calls the function like this:

RegisterCallbacks(0, 1, OnCallback, this);

So far in Python I have the below code (relevant section shown only), which crashes Python (no traceback) shortly after the event is triggered and callback run! is printed.

from ctypes import *

class IBSU(object):
    _dll = WinDLL('ibsu.dll')

    _C_CALLBACK = CFUNCTYPE(
        None,        
        c_int,                                         # device handle
        c_void_p)                                      # user context

    _register_callbacks = _dll.IBSU_RegisterCallbacks
    _register_callbacks.restype = c_int
    _register_callbacks.argtypes = (c_int,             # device handle
                                    c_int,             # event type
                                    c_void_p,          # callback function
                                    c_void_p)          # user context

    def _get_c_callback(self):
        def callback(handle,                           # device handle
                     p_context):                       # user context
            print 'callback run!'
        return self._C_CALLBACK(callback) 

    def register_callbacks(self):
        # keep ref to prevent garbage collection
        self._c_callback = self._get_c_callback()

        self._register_callbacks(0,                    # device handle
                                 1,                    # event type
                                 self._c_callback,     # callback function
                                 c_void_p())           # user context

What is the equivalent to this in my Python class that I can send instead of just c_void_p()?

does the value of pointers change if exception occurs during assignment?

Consider the following code where pb is a member of class myclass:

myclass& operator=(const myclass& rhs){
    myclass *pOrig = pb;
    pb = new myclass(*rhs.pb);  //exception occurs here .
    delete pOrig;            
    return *this; 
}

Will the value of pb remain the same or will it change ? Explain.

What is the difference between the address stored and displayed in C and C++?

In C, if I make a variable and print its address like this:

int a;
int main (void) {
    printf ("%p", &a);
    return 0;
}

The output was: 00AA

The same program in C++ using the line:

cout << &a << endl;

The output was: 0x8f970aa

What is the difference between these two?

I compiled both the programs using Turbo C.

Face alignment and Fisher face recognition

I am trying out face recognition with LDA Fisher faces. Since Fisher faces are not rotation invariant, is it a good method to do face alignment before face recognition? Please provide a theoretical/math explanation.

Thanks in advance