How Can I Correctly Use char* as Keys in a C std::map?

Using char* as a Key in std::map

In C , you may encounter an issue when using char pointers (char) as keys in a std::map. This can occur when attempting to create a map using char keys and encountering unexpected behavior.

To resolve this issue, it's important to understand that by default, std::map compares keys using the pointer addresses, not the actual characters they represent. This can lead to incorrect comparisons and unreliable behavior.

To address this, you must provide a comparison functor to the map. A comparison functor is a function that defines how to compare keys. By using a functor that compares the null-terminated strings pointed to by the char* pointers, you can ensure that the map correctly orders and retrieves elements based on their string values.

Here's an example of how to define a comparison functor for char* keys:

struct cmp_str
{
   bool operator()(char const *a, char const *b) const
   {
      return std::strcmp(a, b) < 0;
   }
};

Once you have defined the comparison functor, you can pass it as the third template parameter to the std::map. This will force the map to use the functor for comparing keys:

map<char *, int, cmp_str> BlahBlah;

By providing a comparison functor, you instruct the map to compare the actual strings pointed to by the char* keys, ensuring correct sorting and retrieval of elements based on their string values.

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