C++ use iostream inside class

Question

I'm using iostream and map. When I try to set the functions, they throw an error.

My code:

#include "string"
#include "iostream"
#include "map"

using namespace std;

class myClass {
    map<string, string> Map;
    Map["Ziv"] = "Sion";

    cout << Map["Ziv"];
};

My error:

error: 'Map' does not name a type
error: 'cout' does not name a type

Why I can't use iostream and cout?

This isn’t the problem, but `#include` directives for standard library headers should use angle brackets, not quotes. So, `#include `. — Pete Becker, Dec 08 '20 at 20:38
@ZivSion "_But I want to make a class_" Doesn't matter what you want: 1) `main` entry point is always a free-standing function. 2) all executable code needs to be in a function. Even if said function is a member of a class. — Algirdas Preidžius, Dec 08 '20 at 20:38
`main` can't be a class. It has to be a function. What you have here isn't a class anyway; it's just a function that you've tried to call a class. — Miles Budnek, Dec 08 '20 at 20:39

eerorika · Accepted Answer · 2020-12-08T20:41:28.237

10

Why I can't use iostream and cout?

Because a class cannot (directly) contain expression statements. It can contain only member declarations.

Expression statements can only be within functions. This would be correct for example:

class main {
    map<string, string> Map;

    void example_function() {
        Map["Ziv"] = "Sion";
        cout << Map["Ziv"];
    }
};

edited Dec 08 '20 at 20:41

answered Dec 08 '20 at 20:37

eerorika

232,697
12
197
326

3

@ZivSion _"I am pretty new"_ Then this should interest you: [The Definitive C++ Book Guide and List](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) – πάντα ῥεῖ Dec 08 '20 at 20:41
1

So this is not a good question and should have been closed (or tagged duplicate) but because the OP set a bounty, it now lead to a +9 answer. IMHO This seems like something inherently wrong with the site... – JHBonarius Dec 21 '20 at 10:55

Adityan.P · Answer 2 · 2020-12-20T05:46:43.840

0

you can't have a C++ progran without the main function so please create int main(){}. And change the double quotes in the #include directives to angle brackets like below:

#include <string>
#include <iostream>
#include <map>

using namespace std;

class myClass {
    public:
         int myFunc();
};

myClass :: int myFunc(){
       map<string, string> Map;
       Map["Ziv"] = "Sion";

       cout << Map["Ziv"]; 
}

int main(){
myClass myclass;
myclass.myFunc();

return 0;
}

Please consider i am a beginner and forgive my mistakes if any.

edited Dec 20 '20 at 05:46

answered Dec 19 '20 at 05:43

Adityan.P

102
3
10

[Why is “using namespace std;” considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) – Gary Strivin' Dec 19 '20 at 15:52
@GaryNLOL ```using namspace std;``` is considered bad practice because when we have a complex program with multiple namespaces ```using namespace std;``` can lead to confusion regarding methods of the ```std``` namespace and other namespaces. – Adityan.P Dec 20 '20 at 05:45

score 0 · Answer 3 · answered Dec 21 '20 at 09:13

In object oriented languages, like C++, you can't write expressions/statements in a class. You may want to use a function. Example:

#include<iostream>
using std::cout;

class Example {
public:
   void sayHello() {
      cout << "Hello!";
   }   
}

int main() {
   new Example().sayHello(); // Prints Hello!
}

score 0 · Answer 4 · answered Dec 21 '20 at 09:33

0

You have to enter the cout in a function, inside the class you can't execute functions, you just can describe them or variables / objects.

answered Dec 21 '20 at 09:33

Max Kofler

86
4

score 0 · Answer 5 · answered Dec 21 '20 at 10:47

Class is an Entity which contains related data members and the operations to modify or access those data members. No expression can be executed within the class. It does not make an sense to do something that you can not access. Because the only way to access and modify something are operations.

Yes in case if you want to print something when the class object is created, you can do that in Constructor. May be this is what you want to do:

#include <map>
#include <iostream>
#include <string>

class myClass {
private:
    std::map<std::string, std::string> Map;
public:
    myClass(const std::string& key, const std::string& value){
        Map[key] = value;
        std::cout << value;
    }
};

int main(){
    myClass cls("Ziv", "Sion");
}

C++ use iostream inside class

5 Answers5