Why I Cannot Cout a String

Why I cannot cout a string?

You need to include

#include <string>
#include <iostream>

Cant cout a string

Besides including the <string> header as mentioned, I think the rest needs to be fixed, like follows:

#include <iostream>
#include <string>

class person {
    class address {
    public: // <<<<<<<<<<<<<<<
        std::string addr;
        int pobox;

        address() {
            addr = "Some Address";
            pobox = 200;
        }
    };

    address a;

public: // <<<<<<<<<<<<<<<
    void Test() {
        std::cout << a.addr;
    }
};

int main() {
    person p;
    p.Test();
    return 0;
}

_{See the Live Demo.}

You'll need to make the class members in question publicly visible, to instantiate or call them.

You may declare address as a nested type of person (at least public to become useful), though I'm not so sure that this is such a good idea.

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The much better approach seems to be declaring a own, self contained address class outside of person, and have the latter one contain a member for it:

class address {
public:

    address() : addr_("Some Address"), pobox_(200) {}

    const std::string& addr() const { return addr_; }
    void addr(std::string value) { addr_ = value; }

    int pobox() const { return pobox_; }
    void pobox(int value ) { pobox_ = value; }

private:
    std::string addr_;
    int pobox_;
};

class person {
    address a_;
public:
    void Test() {
        std::cout << "Address: " << a_.addr() << std::endl;
        std::cout << "PO Box : " << a_.pobox() << std::endl;
    }
};

int main() {
    person p;
    p.Test();
    return 0;
}

_{See another Live Demo.}

why I can't cout after using string tokenizer

Sooner or later ptr=strtok(NULL," ") will return a null pointer. Which you immediately try to output leading to a null-pointer dereference and undefined behavior (and a very probable crash).

I suggest you modify your loop to something like this:

char *ptr = std::strtok(s, " ");
while (ptr != nullptr)
{
    std::cout << ptr << '\n';
    ptr = std::strtok(nullptr, " ");
}

Note the order in which things are done, and which guarantees that ptr will never be a null pointer when you output it.

Why can't I dereference and cout this string in C++

On some compilers <iostream>happens to also include the <string> header. On other compilers, specifically the Microsoft compiler, it apparently does not. And the I/O operators for strings are declared in the <string> header.

It is your responsibility to include all the needed headers, even if the code sometimes happen to work anyway.

So the fix is to just add

#include <string>

at the top of the file.

Cout will not print my string

If your cities are numbered 1, 2, 3, then printcities will be a string containing three characters, of value '\0x01' '\0x02' and '\0x03'. This won't print well. If you were trying to get printcities to hold "123", you either need a stringstream, or std::to_string().

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