I think I have coded everything correctly in this program but still getting errors.
The object si it says it's not accessible.
#include<conio.h>
#include<iostream.h>
class s_interest
{
int p,t;
float r;
s_interest(int a, int b, float c)
{
p=a;
r=b;
t=c;
}
void method()
{
int result=(float)(p*t*r)/100;
cout<<"Simple interest:"<<result;
}
};
void main()
{
int pr,ti;
float ra;
cout<<"\n Enter the principle, rate of interest and time to calculate Simple Interest:";
cin>>pr>>ti>>ra;
s_interest si(pr,ti,ra);
si.method();
}
When the compiler tells you that something is not accessible, it's talking about the public: vs. protected: vs. private: access control. By default, all members of a class are private:, so you cannot access any of them from main(), including the constructor and the method.
To make the constructor public, add a public: section to your class, and put the constructor and the method there:
class s_interest
{
int p,t;
float r;
public: // <<== Add this
s_interest(int a, int b, float c)
{
...
}
void method()
{
...
}
};
Default member access for a class is private (whereas the default for struct is public). You need to make the constructor and method() public:
class s_interest
{
int p,t; // private
float r; // also private
public: // everything that follows has public access
s_interest(int a, int b, float c) { .... }
void method() { ....}
};
Note also that void main() is not standard C++. The return type needs to be int, so you need
int main()
{
...
}
And finally, iostream.h is not a standard C++ header. You need to include <iostream> if you are using a standards compliant C++ implementation.
Following High Integrity C++ Coding Standard guidelines, always declare first public, then protected and private members. See Rule 3.1.1 of hicpp-manual-version-3-3.pdf
All the variables & functions in your class are private. This is the default when access is not specified with the private: , protected: and public: specifiers. I suggest you have a good read of a tutorial - google C++ classes.
also it is int main() and never void main()
The problem is due to access specifiers. By default class methods and data members are private. Make your data members private and methods public. so you can set the private data members value using public methods.
class{
private:
int a;
int b;
int c;
public:
void method();
void print_sum();
};
Related
I am just wondering what this message means on visual studio. Does this mean that by default variables inside classes are set to private. I cannot get a clear answer to this question anywhere.
This is my code:
#pragma once
class number
{
private: // <-- that is grey in the IDE and it shows the text box when you hover over it
int random_number;
public:
number(int x);
int get_number() const { return random_number; }
void set_number(int number) { random_number = number; }
~number();
};
If you don't specify anything, private is implicit when you define a class by means of the class keyword. In other terms, the following definitions are identical:
class C {
int i;
};
class C {
private:
int i;
};
The opposite is true if you use the keyword struct instead of class:
struct C {
int i;
};
struct C {
public:
int i;
};
That is, Visual Studio is telling you that the private is superfluous. Your data member is a private one in both cases.
You probably accidentally wrote public or private two times consecutively. And the second access specifier does nothing.
Variables inside classes are set to private by default and variables inside structs are set to public, so this can be the cause of the message too.
Let's say that I have this class in C++:
class ExampleClass{
private:
int example_var;
public:
void exampleMethod(){
example_var = other_value; // other value will be always different
}
}
How can I unit test exampleMethod()? I would like to do something like this:
void testExampleMethod(){
ExampleClass obj;
int before_call_value = obj.example_var;
obj.exampleMethod();
int after_call_value = obj.example_var;
ASSERT_NOT_EQUALS(before_call_value, after_call_value);
}
But example_var is private.
So, what is the right way to do this unit test? How can I test if a private example_var has changed?
Short answer: Dont do it.
Your test should test against the public interface only. Let me try to explain with some code:
class Adder {
int a,b;
public:
Adder() : a(0),b(0) {}
void set(int x,int y) { a=x;b=y; }
int get() { return a+b; }
};
and a test (assume for a moment we had access to a and b):
void testAdder(){
Adder add;
int a = 1;
int b = 2;
add.set(a,b);
ASSERT_EQUALS(add.a,a);
ASSERT_EQUALS(add.b,b);
ASSERT_EQUALS(add.get(),a+b);
}
Suppose you already distributed the code and someone is using it. He would like to continue using it but complains about too much memory consumption. It is straightforward to fix this issue while keeping the same public interface:
class Adder {
int c;
public:
Adder() : c(0) {}
void set(int x,int y) { c = x+y; }
int get() { return c; }
};
That was easy, but the test will fail :(
Conclusion: Testing private implementation details defeats the purpose of testing, because each time you modify the code it is likely that you also have to "fix" the test.
It is bad approach to test private variable/methods. But if you need there are a lot of options:
You can make Your test class as friend of ExampleClass
You can grab information using moc object
If you want to access example_val, there are one of two things you can do. The first is by making testExampleMethod() a friend method, as follows:
class ExampleClass{
private:
int example_var;
public:
void exampleMethod(){
example_var = other_value; // other value will be always different
}
friend void testExampleMethod(); //Now you can use the function as is.
}
On the other hand, you could just add a getter to your ExampleClass to access the variable, such as the following:
class ExampleClass{
private:
int example_var;
public:
void exampleMethod(){
example_var = other_value; // other value will be always different
}
inline void getExampleVar() const { return example_var; }
}
And then change testExampleMethod() to:
void testExampleMethod(){
ExampleClass obj;
int before_call_value = obj.getExampleVar();
obj.exampleMethod();
int after_call_value = obj.getExampleVar();
ASSERT_NOT_EQUALS(before_call_value, after_call_value);
}
I would honestly use the second method, since accessing a class's private variables is generally not recommended.
You just simply implement get function for that private variable you want to get.
class ExampleClass{
private:
int example_var;
public:
void exampleMethod(){
example_var = other_value; // other value will be always different
}
int GetExampleVar(){
return example_var;
}
}
And call it like
void testExampleMethod(){
ExampleClass obj;
int before_call_value = obj.GetExampleVar();
obj.exampleMethod();
int after_call_value = obj.GetExampleVar();
ASSERT_NOT_EQUALS(before_call_value, after_call_value);
}
Or make testExampleMethod friend function (friend function can access private variables of friend class even if its not its method).
class ExampleClass{
private:
int example_var;
public:
void exampleMethod(){
example_var = other_value; // other value will be always different
}
friend void testExampleMethod();
}
In my opinion first example would be more suitable, but if you cannot modify ExampleClass, you can turn off access control for gcc -- -fno-access-control.
A few options I can think of:
1) Make the test code a friend of the class. That way it can access the private members.
2) Add a getter to the class that's under a #ifdef Testing directive that only gets defined when building the test version (or put public: under that macro and a private: in the #else branch).
3) #define private public when building the test (no, not really).
4) Use gcc's -fno-access-control flag when building the version to test, so that everything is public (if you are using gcc that is).
5) Just give up testing externally from the class and instead add relevant static_asserts/asserts to the class itself to test invariants.
6) Don't. Just stick to testing the public interface.
Hope that helps :-)
I am not sure is my question is right or not? But let me still try to ask once.
I have a Class with have few member variables defined. As per OO concepts, every member function can access , all member variables of its class.
But I want these member variable to be accessed via specific methods (Lets say Getters) , even within same class member functions.
It there any way to do it?
class A {
public:
void func1();
void func2();
B getB();
private:
B b;
}
void A::func1() {
b.functionFromB(); // function uses member variable b directly
}
void A::func2() {
B b1=getB(); // function ask for B from a function and then uses it. // I need something like this... And ensure each function uses same way otherwise there should be warning...
b1.functionFromB();
}
Thanks,
Kailas
No, there is not. You can do it via encapsulation and inheritance like:
class shape
{
private:
int angles;
protected:
shape(int angles_):angles(angles_){};
int getAngles() const;
}
class square : private shape
{
public:
square():shape(4){}
void doSth()
{
\\ you can access angles only via getAngles();
}
}
Any private members of the class can be accessed from within the class, but not by users of the class. So it looks like you need private members and public methods that allow access to them.
class A
{
private:
int a;
public:
int getA() {return a;}
};
int main()
{
A inst;
int t;
inst.a =5; // error member a is private
t = inst.getA(); //OK
}
The concept extends fine to nested class declarations in case you only want to allow instance of a class to be created from another class; details here
As others have said - you have to add an additional layer.
If you want to give access to specific methods then you can use the friend keyword. E.g.
// Public.h
#pragma once
class Public
{
public:
Public();
int GetI() const;
float GetF() const;
private:
std::unique_ptr<Private> p_;
};
//Public.cpp
#include "Public.h"
Public::Public()
: p_(new Private)
{
}
int Public::GetI() const
{
return p_->i_;
}
float Public::GetF() const
{
return p_->f_;
}
// Private.h
#pragma once
class Private
{
friend int Public::GetI() const;
friend float Public::GetF() const;
int i_;
float f_;
};
Keep in mind that every friend method can access ALL private members.
If you really really want to limit which methods can access which members then you can wrap each member in a separate class/struct and make only the getter/setter of that member a friend of that class/struct but I would not recommend this approach.
I am not able to find a similar question else where on this site, but is it possible to declare a class over two different files.
for example, all public class components in a file and privates and others in a different file.
publics.h
class test {
public:
int geta();
void seta(int);
};
privates.h
class test {
private:
int a;
};
The above way is definitely wrong, but is there any such method.
There is a way to get something quite similar: private inheritance.
// private.hpp
class test_details {
protected:
int a;
};
// public.hpp
#include "private.hpp"
class test : private test_details {
public:
int geta() const { return a; }
void seta(int i) { a = i; }
};
Note that you will still need to (indirectly) include the private header in any module that uses the public class, so you're not really hiding anything this way.
Not like that, but the pimpl idiom (or opaque pointer, or Chesshire cat) can help you achieve similar functionality - you can provide a public interface where all implementation details are hidden in an implementation member.
C++ doesn't support partial classes.
Also, note that what you have there are class definitions, not declarations. C++ mandates that if multiple definitions of a class are available, they must be identical, otherwise it's undefined behavior.
This is a good use case for an abstract base class
//File test.h
class test {
public:
virtual ~test() {}
virtual int geta()=0;
virtual void seta(int)=0;
};
//File test_impl.h
class test_impl : public test {
public:
int geta() { return a; }
void seta(int a ) { a = v; }
private:
int a;
};
Here's the declaration:
class a{
public:
void print_fib(int x){
printf("%d\n",b::getfib(x));
};
};
class b{
public:
void init(); //calculate the Fibonacci numbers, save them in `fib[]`
int getfib(int x);
private:
int fib[10];
};
class c{
private:
a ca;
b cb;
};
How can I access cb.getfib() from ca.print_fib()?
Re-order, else forward declare
class b{
public:
bb();
};
class a{
public:
aa(b& inst);
};
class c{
private:
a ca;
b cb;
public:
void foo()
{
ca.aa(cb);
}
};
// implement here
void a::aa(b& inst)
{
// do stuff
b.bb(); // voila
}
A better design decision may be to execute b::bb() in c::foo() and pass the result to a::aa().. then they can be independent...
If you pass this to ca and cb, you can use it to access cb and ca respectively.
class a {
public:
a(c *parent) : _parent(parent) {}
aa() { parent->cb.bb(); }
private:
c *_parent;
};
class c {
public:
c() : ca(this), cb(this) {}
...
if all three classes are in same file, your code should work fine.
however, if you have separate header files, include these header files into file that contains class C.
Prefer Ed Heal's comment over my answer.
The main issue I see in the code as I see it now is the call to b::getfib(x) from a::print_fib which is not the correct way to make this call.
The function in b is not static, and cannot be unless the "cache" is also made static. Therefore to call it you need an instance of b (which you have in c). You could pass that into your function in a, but really in this case I do not see why you would need multiple instances of b.
Note also that from your code, b has not been declared yet in the header of a. Your code must be rearranged to ensure dependencies are correctly handled.