changing key values of all elements in a multimap container [closed] - c++

Question

Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 3 years ago.
Improve this question
I am working on a c++ code which includes a command schedule. I implement the schedule as a multimap container, with execution time,as the key, and command name I want to execute. I need to be able to time shift all the commands in the schedule.
I assume I can do that by copying the container to another container and erasing the original container, then changing the key values for each pair in the copy container and inserting it back in the original container, like the example code below.
#include <stdio.h>
#include <map>
int main() {
std::multimap<int,int> original,copy;
original.insert(std::pair<int,int>(10,1));
original.insert(std::pair<int,int>(10,2));
original.insert(std::pair<int,int>(12,3));
std::multimap<int,int>::iterator it;
copy=original;
it=original.begin();
original.erase(it,original.end());
int tctime;
int command;
for (it=copy.begin();it!=copy.end();it++){
tctime =(*it).first+5;
command=(*it).second;
original.insert(std::pair<int,int> (tctime, command));
}
return 0;
}
while this works, I would like to know if there is a better solution to implement it.

Answer 1

Although you should ask these kind of questions on Code Review, I will write my answer here also so it may help someone else (and since it is not yet closed).
First, since your question has a C++ tag, please use #include <iostream> instead of #include <stdio.h>.
Second, I suggest you to use std::make_pair instead of the std::pair constructor. std::make_pair automatically deduces types of the values passed to it so I would prefer it over std::pair where you need to specify the types. So, you should use something like this:
original.insert(std::make_pair(10,1));
Next, since you are erasing all the values from the std::multimap<int,int> original, why not just use std::multimap::clear? It is less code to write and your intention is more straightforward.
original.clear()
instead of
it=original.begin();
original.erase(it,original.end());
Furthermore, I would suggest using range-for loops over the standard loops.
for (auto const& it : copy) {
tctime = it.first +5;
command = it.second;
original.insert(std::make_pair(tctime, command));
}
instead of
for (auto it = copy.begin(); it != copy.end(); it++){
tctime =(*it).first+5;
command=(*it).second;
original.insert(std::pair<int,int>(tctime, command));
}
And the last thing, good practice would be to initialize variables tctime and command to 0.
Full code:
#include <iostream>
#include <map>
int main() {
std::multimap<int,int> original,copy;
original.insert(std::make_pair(10,1));
original.insert(std::make_pair(10,2));
original.insert(std::make_pair(12,3));
copy=original;
original.clear();
int tctime = 0;
int command = 0;
for (auto const& it : copy) {
tctime = it.first +5;
command = it.second;
original.insert(std::make_pair(tctime, command));
}
return 0;
}
Here is the fully refactored code live.