Initialize a map with map-values

Question

I want to initialize a map with map-values in the following way:

std::map<int, std::map<int, int>> map =
{
    { 1, { { 1, 0 }, { 2, 1 } } },
    { 2, { { 1, 1 }, { 2, 0 } } },
};

While this compiles without any error or warning, it raises an exception stating "map/set iterators incompatible". If I remove the second pair, i.e. { 2, { { 1, 1 }, { 2, 0 } } }, no exception is raised and map contains one pair with key 1 and a map containing the pairs (1, 0) and (2, 1) as its value.

I'm sure there is a quite good reason for this (at first glance) somehow strange behavior.

Solution

Nope, there's no good reason. It turned out to be one of the beautiful bugs in Visual Studio 2013.

It [works for me](http://coliru.stacked-crooked.com/a/ef37b18f0a8f1c83)... perhaps it is a bug with your compiler. — Mankarse, Jun 03 '14 at 13:12
hehe, the OP is right it breaks in VS. It's a bug. VS2013 has several issues with nested initializers lists. I think is fixed in update 1. — 101010, Jun 03 '14 at 13:23
@0xbadf00d LOL it's OK with me, I don't want to keep lovers apart. — 101010, Jun 03 '14 at 13:28
Duplicate of [this one](http://stackoverflow.com/questions/23965565/how-to-do-nested-initializer-lists-in-visual-c-2013) (but I can't mark it as such because that question has no answers). @40two There's no *bad habit* in using trailing commas. They're quite convenient because you don't have to modify existing lines when adding a new initial value. Also extremely handy if you're ever writing a tool to autogenerate initial values. — Praetorian, Jun 03 '14 at 13:38
@40two: Beyond convenience, I'd say that they are a *good* practice, as they allow line-based diffs to be significantly cleaner. — Mankarse, Jun 03 '14 at 14:32
If this is the answer, please answer your own question. With details if possible. — david.pfx, Jun 03 '14 at 14:59

score 0 · Answer 1 · answered Jun 05 '14 at 14:02

did you tried with c++11 option?

#include <iostream>
#include <map>

int main()
{
  std::map<int, std::map<int, int>> map =
    {
      { 1, { { 1, 0 }, { 2, 1 } } },
      { 2, { { 1, 1 }, { 2, 0 } } },
    };

  auto t = map[1];
  std::cout << t[1] << std::endl;
  std::cout << t[2] << std::endl;

  auto t2 = map[2];
  std::cout << t2[1] << std::endl;
  std::cout << t2[2] << std::endl;

  std::cout << "--------------" << std::endl;
  std::cout << map[1][1] << std::endl;
  std::cout << map[1][2] << std::endl;
  std::cout << map[2][1] << std::endl;
  std::cout << map[2][2] << std::endl;
}

Initialize a map with map-values

Solution

1 Answers1