chapter 9 exercise problem 1

fortran_ii · March 26th, 2010, 02:25 PM

Regarding Chapter 9 exercise problem 1:
The question is âWhatâs wrong with the following code?â â¦, and is not âhow should the class be rewritten to improve it?â.

The online SOLUTION offers:
// Soln 9_1

/*
CBadClass initializes the member p in the contructor with the address passed as the argument.
The argument to the constructor could be a string allocated on the heap that could be
destroyed externally. This would leave the object with an invalid pointer.
The constructor should copy the argument and there should be a destructor to release the memory for p.
It is also possible the argument to the constructor could be null.
The default constructor does not initialize the members at all.
The class would be better defined as below.

*/
#include <cstring>

class CBadClass
{
private:
int len;
char* p;
public:
CBadClass(const char* str=0):len(0)
{
if(p)
{
len = strlen(str);
p = new char[len+1];
strcpy_s(p, len+1, str);
}
}
};

When I started to think about how to answer the exercise question, before I looked at the on-line solution, my thought was along the lines of the above, with the main thing being that the string is not copied into an array that is inside the class.

After thinking more about it, my conclusion was, and is, that the main thing wrong with original class is that there is no way to access p in any code that incorporates the class, because p is private, and the original class provides no other means of indirectly accessing p. Given that, the on-line solution is at best incomplete.

Do you agree? Did I miss something?

chanjackman · December 20th, 2011, 10:31 PM

1. Even I corrected the Ex10_02 as the Errata showed, I still failed
2. Could anyone tell me how to do this exercise from the begining?
3. I used:
a. file>new project
b. CLR empty project
c. (right click of source files ) Add existing item from the code of CH10_02.
d. (right click of header files) Add existing item (person.h) from the
code of CH10_02
e. run the Ex10_02.cpp
f. fail.

crina · December 21st, 2011, 05:38 AM

I have an asp.net application(MVC) that run on blackberry.In this I have a grid and when user click on a row of the grid i get value from a column that is hidden and i want to show in a textarea.

This is the control that i should click:

Code:

       <td   colspan="3"> 
    <a id="ModelS<% = Model.Id  %>" href="#"  onclick ="javascript:ShowBody('B<% = Model.Id  %>')">
        <%=Model.Subject%>
        </a></td>

This is the code for control that i shoult read :

Code:

     <td  id="B<%=Model.Id%>" style="display: none; " > 
         <%= Model.Body%>
    </td>

When I click i run function :

Code:

         function ShowBody(stringId) {
             var obj1
             var obj2

             obj1 = document.getElementById(stringId);
             obj2 = document.getElementById("BodyMessDetailed");

             obj2.value = obj1.innerText;
            
         }

and here must arrive the information:

Code:

      <textarea id="BodyMessDetailed"  readonly="readonly" cols="1" rows="10" name="TT"
                      style="width:98%;height:90%; overflow:scroll;" 
                      >
      </textarea>

I checked and if i put a string instead obj1.innertext goes ok .But If I let obj1.innertext ,doesn't put anything.I try with value, textcontent but also doesn't work.

Can somebody help me ?