Question

I have a question about std::map structure:
this code fragment works correctly:

map<string,int> mappa;
int main(int argc, char** argv) {
mappa["b"]=1;
mappa["a"]=2;
 for(std::map<string,int>::iterator it=mappa.begin();it!=mappa.end();++it )
{
    cout<<it->first<<"\n";     
} 
return 0;
}

output:

a
b

but if I do:

map<string,int> mappa; 
std::map<string,int> getList(){
return mappa;
}

int main(int argc, char** argv) {
mappa["b"]=1;
mappa["a"]=2;
for(std::map<string,int>::iterator it=getList().begin();it!=getList().end();++it )
 {
    cout<<it->first<<"\n";   
 } 
return 0;
}

my output is just

b

why?
Thanks!

Answer 1

You are calling getList multiple times. Each time it creates a new map using the copy constructor.

You such do this:

std::map<string,int> myList = getList();
const std::map<string,int>::iterator myListEnd = myList.end();
for(std::map<string,int>::iterator myList.begin();it!=myListEnd;++it )
{

I am assuming that you require a copy.