Is it possible to reuse variable names with using namespace?

Question

For example, initially I have a sample program:

#include<iostream>
#include<algorithm>
using namespace std;
int main() {
    int a[3];
    sort(begin(a),end(a));
    cin;
}

Now I want to modifystd::cin(to provide more functions like invoke a function when input fails). So I introduces a headermystd.h like:

#include<iostream>
#include<algorithm>
//begin of mystd.h
namespace mystd {
    struct cin_wrapper {

    }cin;
}
//end of mystd.h
using namespace std;
int main() {
    int a[3];
    sort(begin(a),end(a));
    mystd::cin;
}

But the change seems to be not convenient.(Users must mention all components using std::sort;using mystd::cin; or replace all cin with mystd::cin. using namespace std;using mystd::cin; causes the cin ambiguous)

In fact I'm going to write a modified standard library and make the use of it as convenient as the original one. The ideal code I wish users can write is:

(PS: this means mystd can be just used as std, not indicates I want to encourage users to use using namespace everywhere)

#include<iostream>
#include<algorithm>
#include "mystd.h"
using namespace mystd;
int main() {
    int a[3];
    sort(begin(a),end(a));//std::sort
    cin;//mystd::cin
}
//or
int main() {
    int a[3];
    mystd::sort(mystd::begin(a),mystd::end(a));//sort, begin, end from std
    mystd::cin;
}

I've tried to add using namespace std; in mystd but it also causes ambiguity.

One complicated solution I can image is to create a using statement like using std::string; in mystd for all std members not modified.

Is there a more practical way for me to implement mystd.h?

Answer 1

If you really insist on doing this, you can manage to do so by introducing your using statements at nested scopes. For example:

using namespace std;

int main() {
    using namespace mystd;

    int a[3];
    sort(begin(a), end(a));//std::sort
    cin_wrapper w;//mystd::cin
}

Anything involving using namespace std; should be avoided though (using other, more restricted namespaces isn't so bad, but that one is a huge truckload of cans of worms you're opening).