I want to take inputs of 2d vector using ranged based for loop. How can i do?-CodePudding

As a beginner i am exploring multiple methods to increase my clarity, so i did this question.

// no problem with this looping method
vector <vector<int>> vec(n,vector<int>(m));
for(int i = 0; i < n; i  ){
    for(int j = 0; j < m; j  ){
        cin >> vec[i][j];
    }
}

// but i tried in this way using ranged based loop, and it doesn't work. 
// I think i need a few modification here, so i need your help.
for(vector<int> v1d : vec){
    for(int x : v1d){
        cin >> x;
    }
}

Same code, just cin replaced by cout, i can print that vector elements easily. but in case of cin i am having problem. no error, but it's not working.

Thanks

CodePudding user response：

You need to take the values by reference in the range base for-loops. Otherwise v1d and x will be copies and any changes you make to those copies will not be affecting the content of vec in any way.

for(auto& v1d : vec) {   // or: std::vector<int>& v1d
//      ^
    for(auto& x : v1d) { // or: int& x
//          ^
        std::cin >> x;
    }
}