切换案例中地图迭代器的交叉初始化

Question

Recently i was trying out a program using std::map and came across a situation where I needed to use the map iterator in a switch case. My program goes like this :-

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <set>
#include <map>
#include <algorithm>
using namespace std;


int main() 
{
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    map<string,int> m;
    //map<string,int>::iterator itr;
    int q, mark, type;
    string name;
    cin >> q;
    while (q--)
    {
        cin >> type;
        switch (type)
        {
            case 1: cin >> name >> mark;
                    m[name] += mark;
                    break;
            case 2: cin >> name;
                    m.erase(name);
                    break;
            case 3: cin >> name;
                    auto itr = m.find(name);
                    if (itr != m.end())
                        cout << itr->second << '\n';
                    else
                        cout << "0";
                    break;                             // problem lies here
            default: cout << "ERROR !!!\n"; break;
        }
    }
    return 0;
}

For this code my compiler flashes an error :-

Error] crosses initialization of 'std::_Rb_tree_iterator<std::pair<const std::basic_string<char>, int> > itr'

If I declare the iterator itr outside the switch case then the codee compiles properly. Can anyone tell me what's wrong in this method ???

Answer 1

You should consider that in C and C++ a switch is implemented based on goto and you are not allowed have a goto skipping the initialization of an object.

Just wrap each case in a block { ... } and everything should be fine. The case creating the problem is the one with the itr .

switch (type) 
{
    case 1: {
        cin >> name >> mark;
        m[name] += mark;
        break;
    }
    ...
    case 3: {
        cin >> name;
        auto itr = m.find(name);
        ...
        break;      
    }
    ...
}