VS2010 woes: tuples as map keys

elbeno, 20 February, 201530 June, 2015

Another day, another compiler/library bug. If you’re unfortunate enough to still be using Visual Studio 2010, don’t use tuples as map keys.

#include 
#include 
#include 

using namespace std;

typedef tuple FooT;
typedef map MapT;

int main(int, char*[])
{
  MapT m;

  // put a value in the map
  {
    FooT f(nullptr, 0);
    m[f] = 1337;
  }

  // retrieve a value
  int s;
  {
    FooT f(nullptr, 0);
    auto i = m.find(f);
    if (i != m.end())
    {
      // VS2010 says:
      // error C2440: 'initializing' : 
      // cannot convert from 'const FooT' to 'int *'
      s = i->second;
    }
  }

  return 0;
}

C++ Programming

Comment

Alan says:

20 February, 2015 at 12:11 pm
Something odd… if i replace
```
m[f] = 1337;
```
with either
```
m.insert(std::make_pair(FooT(nullptr, 0), 1337));
```
or
```
m.insert(std::make_pair(f, 1337));
```
It works fine (compiles and behaves like it should at runtime), even though the error reported by VS when it doesnt work points at the s assignment line!

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