std::map proper use?

[bkelly]

Environment Windows XP Pro, Visual Studio, C++, MFC
After examining some code I use to put data in a map I have become concerned that I may be inserting data improperly. The map for parameters is defined as:

struct td_parameter_definitions
{
CString          name;
unsigned ing  tag;
...
};

typedef std::map< td_parameter_key, td_parameter_definitions > td_parameter_map;

The parameter map is within a message structure. The address of the message structure is handed to a method that reads a text file and fills in data. It creates a local pointer to the parameter map and sets fields within the parameter structure as follows:

Read_parameter_Definitions( st_msg_data *p_msg_data )
{ ...
   // make a short hand name for the parameter map
td_parameter_map *p_parm_map = p_msg_data->parameter_map;
parameter_number = <an integer value>;
...
       // cs_t1 is filled in by some additional code not shown here.
( *p_parm_map)[parameter_number].name = cs_t1; 
// etc
... }

My problem is that I realized that I was not explicitly adding entry [parameter_number] to the map. The code just jumped up and starting putting data in that entry as though it already exists. I am finding that rather worrying.

Since the map is defined as a map of structures and not defined as a map of pointers, does the simple act of referencing entry [1] (for example) create that entry. If so, then is it OK for the code to proceed to set various fields of that entry.

Is that a back door to creating an entry in a map that I should not use?