So here is my code, I find the sort doesn't work for the vector in this map. Does anyone has the idea? The output of this code is still "3 1 2 4 5"
map<int, vector<int> > values;
values[1] = {3,1,2,4,5};
for(auto g: values) {
sort(g.second.begin(), g.second.end());
}
for(int i=0;i<values[1].size();i ) {
cout<<values[1][i]<<" ";
}
CodePudding user response:
You need to use a referenced type in the range based for loop
for(auto &g: values) {
sort(g.second.begin(), g.second.end());
}
Otherwise the range based for loop deals with copies of elements stored in the map.
If your compiler supports the C 17 you can also write
#include <vector>
#include <map>
#include <iterator>
#include <algorithm>
//...
for (auto &[key, v] : values)
{
std::sort( std::begin( v ), std::end( v ) );
}
CodePudding user response:
auto g: values
takes the value of an element of values
but does not allow you to change the contents in values
.
auto &g: values
takes a reference to an element of values
which allows you to change the contents of values