in c++ std library, assigning to a map element at index -1

Question

I see a code below. (it's from caffe source, a deep learning library)

  map<int, string> layer_idx_to_layer_name;
  layer_idx_to_layer_name[-1] = "input";

What does the second line mean? I guess it's assigning a default value. Is it correct?

score 3 · Accepted Answer · edited May 23 '17 at 12:08

3

It's doing what it says: Assigning the string "input" to the map entry whose key is -1.

There's no concept of a default value with std::map.

Remember, the key of a std::map doesn't have to be an int (let alone, positive ints) - it can be pretty much any type. std::map isn't a vector.

edited May 23 '17 at 12:08

Community

answered Jun 08 '16 at 07:59

Roddy

2

The correct term to use would be key (rather than index) – Xiobiq Jun 08 '16 at 08:35
oh, I see, I forgot it -1 is actually a key value. Thanks. – Chan Kim Jun 08 '16 at 08:53
and the key is of type int here(so -1 is valid). and there's no limit in the key range (no need to be continuous, no need to start from 0,..) unlike normal arrays. – Chan Kim Jun 10 '16 at 13:39

1 Answers1