I have never seen anyone pass by const copy and there probably is a reason. I know that the compiler ignores top level const-ness of function arguments. There are functions which take arguments without manipulating those arguments return the result, for example the C Standard Library funcion double sqrt (double x). The function shouldn't modify it's argument, but it can since the argument isn't const.Take these two functions for example:
double square_root_1(double arg)
{
arg = 7; // we won't get the desired results
return arg * arg;
[code]....
So isn't it better to pass by const copy to make sure that you (or someone else) don't by accident modify the argument? The only disadvantage I see is that it makes the code too verbose.
You might notice that the above code doesn't compile, this is the error:
cannot convert parameter 2 from 'BYTE [2][4]' to 'BYTE *' 1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
Even after some search I couldn't really find an answer to my problem, how do I pass the const BYTE array which I declared above in the function as a parameter (or what structure do I need to set for the function as a parameter)?
//This program calls unionLL function which takes list1 and list2 objects of //LinkedList type as arguments also nowhere in the function I had changed List1
//and List2 contents although the list1 and list2 head's and also their next //pointer remain same but the elem or data field is automatically updated to //some garbage value.
#include <iostream> using namespace std; typedef int E; class LinkedList; class Node {
I've been given an assignment with the below questions.
1. What is the difference between pass by reference & pass by pointers?
2. What is the use of the initialization list in the constructor?
3. What is meant by a reference & its advantage?
4. Class has a reference, pointer and a const. Is it possible to write the copy constructor & assignment operator overloading funciton? how? ( Since reference is there, I'm not sure on how to write for it)
5. Example for a variable decleration and definition? (I know for function but for variable don kw how)
6. static and const static what is the difference??
#include <iostream> class Hello { public: void Test() {
[Code].....
As i know a non-constant member function cant be called inside a constant member function but how the above code has been compiled successfully and giving the expected result .
i think i understand both concept. i know that pass by value is that the function receiving those values makes actually a copy of those parameters. Passing by reference makes the variable in the main function to actually see those changes in the other function, instead of a copy, and apply them to the variable in the main function. my question is, why would i pass it by reference if i just can make a return type function.
I have a class that I'm going to use to store a category. Right now there are seven options, but there is the potential for a whole lot more in the future. So I started off by storing an integer as the private member. I then used static constants to define the numeric values to represent each category, then a set of static constant strings that corresponds to those numbers in case I need their actual names. Finally I set up some static functions to convert between the integer value and the string, and vice versa.
I'm not sure if this is the best way to go about this. For one it makes the categories names and designations unchangeable. I thought that storing them in a file would be a better option, but then i needed a container that is the equivalent of a constant.
I thought of defining a class to contain an int and the associated string. It would be designed so that it can only be initialized with both items. Then provide no functionality to change the contents. So I've basically created my own constant.
I was just doing some demo programs and came through the above concept but not able to identify what exactly the need of the above concept . what magic exactly const is doing in the second case ?
Where exactly we can use this concept in real time programming ?
I am trying to use libXl to output text from a C++ program to an Excel file. The problem is coming with this library function:
bool writeStr(int row, int col, const wchar_t* value, Format* format = 0)
Writes a string into cell with specified format. If format equals 0 then format is ignored. String is copied internally and can be destroyed after call this method. Returns false if error occurs. Get error info with Book::errorMessage().
If I give input as a string literal like "Hello World" it is displayed correctly. However, if I try to give input as a variable of type const char*, it displays garbage.
Following is my code. MyCompany::company is a QString.
I am having a problem concerning a static const member variable I want to use to set a certain property of my class during development time. The question actually concerns proper implementation as I do have a solution that "works" at least. The variable should denote the size of a member array which I don't want to allocate on the heap due to serious performance issues. So here is my code:
//MyClass.h class MyClass{ public: static const int MyArraySize = 256; private: int MyArray[MyArraySize]; };
This works but it's not nice for two reasons:
1) It doesn't separate interface from implementation. I would prefer to define the variable in the corresponding .cpp file but it doesn't work:
//MyClass.h class MyClass{ public: static const int MyArraySize;
[Code] .....
If I delete the line int MyArray[MyArraySize]; the above code works but when I use it to define the size of the array I get a "constant expression expected" error for the line int MyArray[MyArraySize]; which makes sense as the compiler does not know the value of MyArraySize when he reaches int MyArray[MyArraySize]; and therefore can not allocate the memory. Of course I can move MyArray to the heap like that:
//MyClass.h class MyClass{ public: static const int MyArraySize; static const int MyValue;
[Code] .....
But as I mentioned before this causes a remarkable loss of performance.
Something like the following does not work:
//MyClass.h class MyClass{ public: static const int MyArraySize = (int) pow(2, 8); private: int MyArray[MyArraySize]; };
This gives a "constant expression expected" error for the line static const int MyArraySize = (int) pow(2, 8);
Interestingly the following code works:
//MyClass.h class MyClass{ public: static const int MyValue; };
//MyClass.cpp #include "MyClass.h" const int MyClass::MyValue = (int) pow(2, 8);
So if I use pow outside of the class definition I get no errors. Is there any solution to those problems? So what I want is: 1) Don't allocate the array on the heap 2) Separate interface from implementation 3) Being able to use functions like pow to define MyArraySize 4) Not use global variables
I've been given specific instructions to create an array inside a Class Matrix using a constant n. This is my class but I am getting errors. I thought that maybe I had to initialize the const and the array using the constructor function Matrix() instead of directly in the class, but I didn't have any luck with that either.
class Matrix { public: Matrix(); private: const int n=3; int e[n][n]; };
