compiler doesn't finish process

Question

I have a multimap which key is short and value is the other multimap

std::multimap<short,std::multimap<short,short>> multimap

now I want to do it`

std::multimap<short,short> &a=multimap.find(0)->second;
std::pair<short,short> z={1,2};
a.insert(z);

It compiles fine. But when I run it it just stops and doesn't finish the process, It even doesn't throw any runtimeerror. Have any ideas? Thanks in advice.

Answer 1

Having

std::multimap<short,std::multimap<short,short>> multimap
...
std::multimap<short,short> &a=multimap.find(0)->second;
std::pair<short,short> z={1,2};
a.insert(z);

If find returns multimap::end that one shall not be dereferenced, but you do and get a reference to second, the behavior is undefined when later to use that reference to insert.

So of course check if find succes, like

  std::multimap<short,std::multimap<short,short>> multimap;
  std::multimap<short,std::multimap<short,short>>::iterator it = multimap.find(0);

  if (it == multimap.end()) {
    ...
  }
  else {
    std::multimap<short,short> &a = it->second;

    std::pair<short,short> z={1,2};
    a.insert(z);
  }

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Out of that your title "compiler doesn't finish process" is not very clear, the execution is not the one you expect, but the compiler does not run the process