programing error in writing own manipulator.

[sridhard2406]

I am trying to create own manipulator, which will add the extra tab with input. Please find when I run the below program I got below mentioned error. could you please anybody help me, what is the wrong with the code?

#include <iostream>
#include <cstdlib>
 
using namespace std;
 
class addtab
{
 
        addtab()
        {
                cout << "constructer has called" << endl;
        }
        ~addtab()
        {
                cout << "destructer has called" << endl;
        }
        public:
        friend ostream& operator<<(ostream& ,int&);
};
ostream& operator<<(ostream &os,int &n)
{
        return os ;
}
 
int main()
{
 
        int n;
        n  = 7;
        cout <<  "this " << addtab(n) << endl;
}
 
when I run this program, I am getting below mentioned error? please help me to clear my error.
 
 
create_own_manu.cpp: In function `int main()':
create_own_manu.cpp:30: no matching function for call to `addtab::addtab(int&)'
create_own_manu.cpp:7: candidates are: addtab::addtab(const addtab&)
create_own_manu.cpp:10:                 addtab::addtab(
)

[newb16]

First, you do not 'run' it - it doesn't even compile, and in order to run it, you need to compile it. As the error message states, you want to use addtab::addtab(int) constructor in line 30, but there is no such constructor declared.

[johny10151981]

Hi,
Not a C++ programmer even though I am trying a bit.

int main()
{

int n;
n = 7;
cout << "this " << addtab(n) << endl;
}

look at cout
you tried addtab(n). Even if you made a constructor that receive an integer as parameter, you will get an error.
why? cause if you call a function or whatever in cout it must have to return something(but not void)(and if I am not wrong). And you cant define any return type for a constructor.

Best Regards,
Johny

[weaknessforcats]

A manipulator must take only one argument, an ostream& and return and ostream&.

ostream& MyManipulator(ostream& os)
{
 
  //do my stuff:
  os << etc....
 
   return os.
 
}

[johny10151981]

oh I forgot to add in the first place

int main()
{

int n;
n = 7;
cout << "this " << addtab(n) << endl;
}

addtab is a class not a object of any class. But It seems that you are tring to use it as variable! Not that clear to me :)

What do you think :)

[sridhard2406]

any body can tell me , can we write the own manipulator in c++, if we can , can you provide some links for Example/ some sample program..

[weaknessforcats]

addtab is a class not a object of any class. But It seems that you are tring to use it as variable! Not that clear to me :)

This is just fine. All objects are variables but some objects can be used as functions. These are called functors and they are classes that implement the function operator, operator()().

can we write the own manipulator in c++, if we can

Yes, but it has have one argument, ostream&, and it must return am ostream&:

ostream& StarBar(ostream& os)
{
os.write("*****", 5);
return os;
}
 
 
cout << StarBar << "--" << StarBar<< endl;

[sridhard2406]

can we write a own manipulater with single argument.

[weaknessforcats]

Yes.

However, your manipulator must have this prototype:

ostream&   MyManipulator(ostream&);

If your manipulator needs input values then you need to get them from elsewhere than through function arguments. You would normally use a Singleton object to get the values or maybe call a function that gets the values for you.

[sridhard2406]

Thanks for all your reply