Wrong order of output while using map in C++ - c++

Question

I have written a program in which certain entries are made into a map. Later, using an iterator, I wanted to see the key-value pairs in this format
key=value.
But the output is coming as
=key value.
Here's the code
int main() {
map<string,string> mp;
int n;
string name, number;
cin>>n;
for(int i=0; i<n; ++i)
{
getline(cin,name);
getline(cin,number);
mp.insert(pair<string,string>(name,number));
}
string line;
map<string,string>::iterator fndr;
fndr = mp.begin();
cout << (*fndr).first << "=" << (*fndr).second;
return 0;
}
Here's the input
2
abhay 239487
hello 23478
Here's the output
=abhay 239487

Answer 1

Your .first is empty and the whole thing is going in .second. getline() is taking the whole string input and storing it in number variable. Quick solution (but won't work for names that contain spaces):
cin >> name;
cin >> number;
Explanation:
Before using getline(), you have used cin >> n to input the number of strings. After the input, when you press Enter a \n is appended at the end of your input. So your input actually looks like this:
2\n
abhay 239487\n
hello 23478\n
Now cin >> n uses 2 in the first line to store it in n variable but the \n is still there in the stream. When getline() is used for the next input, it finds the \n in the input stream and terminates thus storing nothing in name variable (\n is a delimiter for getline()). The next getline() finds the string abhay 239487 before it encounters another \n and terminates.
Thus, we need to ignore the \n after 2 before the first execution of getline()). We can use cin.ignore() between the last cin and the first getline(). This will ignore the next character in the input stream.
Code
int main() {
map<string,string> mp;
int n;
string name, number;
cin>>n;
cin.ignore();
for(int i=0; i<n; ++i) {
getline(cin,name);
getline(cin,number);
mp.insert(pair<string,string>(name,number));
}
string line;
map<string,string>::iterator fndr;
fndr = mp.begin();
cout << (*fndr).first << "=" << (*fndr).second;
return 0;
}
You can notice after using cin.ignore(), abhay 239487 goes in name and hello 23478 goes in number. The output is:
abhay 239487=hello 23478
which is expected for this case.
How to workaround the problem of segregating key: value pair ? There are two ways:
Either you can input the name (key) and the corresponding number (value) in two different lines (This method will work for strings which contains spaces in name) like this:
2
abhay nayar
239487
hello
23478
Or, you can use cin >> name >> number to get those values (but you cannot use names that contain spaces because any whitespace character is a delimiter for cin).