std::map declaration problem

[bkelly]

I am having a problem with the code that inserts an item into a map. I think it is really a decleration problem. I use typedef the set it up because the map is used in two classes.

I cannot cut and paste from my work computer for various reasons so please comment on any typos, but presumed I made an entry error. There is only one compiile error in the program and that is on the line marked as such.

From the .h file:

typedef   int td_msg_parameter_number;
typedef  CString  td_msg_parameter_name;
typedef std::map< td_msg_parameter_number, td_msg_parameter_name > td_map_parameter_names;
typedef std::map< td_msg_parameter_number, td_msg_parameter_name >:: iterator td_iterator_parameter_names;

typedef struct
{  ...
   td_map_parameter_names *pmap_message_parameters;
}

Then from the .cpp file I try to insert a name into the map.
The method Get_Next_Definition(..) reads a line of text from a configuration file and returnes two strings of data. The second string is to be put in the map

void C_Configuration_Manager::Populate_Parameter_Map( td_map_parameter_names * pmap_message_parameters )
{

td_message_parameter_number  parameter_number = 1;
td_msg_parameter_name            cannot_use;
string                                         expected;
string                                         t_string;
bool                                           call_status;

do{
expected = "Parameter";
call_status = Get_Next_Definition( &expected, &t_string );
if( t_string != "End" )
   {
//      cannot_use( t_string.c_str() );  // why not, secondary question
    td_msg_parameter_name local_parameter_name( t_string.c_str() );
        // this compiles

       // I check the help file and added this just to test it.  No compile error
    pmap_message_parameters ->insert( map<int, CString>:: value_type( pararmeter_number, local_parameter_name ) );

          // This is my problem line.
      pmap_message_parameters[ parameter_number ] = local_parameter_name; 
}
} while( t_string != "End" );
}

the error returned is:
Error 1 error C2697: binary "=' : no operator found which takes a right-hand operand of type 'td_msg_parameter_name' (or there is no acceptable conversion)

[kooth]

This is because you are assigning an object and not a pointer.

Your secondary question is related: t_string.c_str() returns a null-terminated string, not a CString.

[bkelly]

I don't understand. the declaration:

typedef   int td_msg_parameter_number;
typedef  CString  td_msg_parameter_name;
typedef std::map< td_msg_parameter_number, td_msg_parameter_name > td_map_parameter_names;
 

I see the map as using an integer as the key and a CString as the item stored. Neither are pointers.

When you say an object and not a pointer are you referring to
pmap_message_parameters[ parameter_number ]
or to
local_parameter_name;

Thank you

[kooth]

Sorry to be unclear (I usualy am to some degree): On line 23, I guess you don't have a copy constructor or operator = for pmap_message_parameters, so the compiler says there isn't one. Try this for the line:

pmap_message_parameters[ parameter_number ] = &local_parameter_name;

The c_str() is not returning a CString, but the data to which that object points ( char *).

[bkelly]

I added the address operator to produce:

pmap_message_parameters[ parameter_number ] = &local_parameter_name;

and the error message changed slightly to:

Error 1 error C2697: binary "=' : no operator found which takes a right-hand operand of type 'td_msg_parameter_name *' (or there is no acceptable conversion)

As I look at the map declaration I don't see that there is a pointer involved. I presume that it will take the local_parameter_name as "by value" (as opposed to "by ref" or "by address") and copy local_parameter_name into the map. I am still seeing this as a declaration problem and don't understand my error.


Edit:
I backed up to the method where I created the map and tried to insert a simple value. That looks like this:

 
    // I start with a structure for a message.  The message contains multiple parameters.
    // the goal is to create a map for those parmeters and use the parameter number
   //  as the key into the map.
p_message_definition->pmap_message_pararmeters = new ( td_map_parameter_names );

    // Create test data to put in the map
td_msg_parameter_name   stuff = _T("stuff" )
td_msg_parameter_number  parameter_number = 1;

    // Now try to add a single entry into the map

p_message_definition->pmap_message_pararmeters[ parameter_number ] = stuff;

Did that simplify the question or did I just add an error on top of another error?

[kooth]

Well bkelly, I guess I'm getting too old for this! :)

Perhaps the problem is with the "left" side: pmap_message_paraameters is a pointer, no?
So maybe the compiler wants (in your original post):

*pmap_message_parameters[ parameter_number ] = local_parameter_name;

or perhaps:

&pmap_message_parameters[ parameter_number ] = local_parameter_name;

[bkelly]

The immediate problem appears to be one of precedence:

(*pmap_message_parameters)[ parameter_number ] = local_parameter_name;

Add in the parens and it compiled. But then, I still didn't have what I needed. I eventually detrermined that I really needed to pass an pointer pointer to a function so it could give me a pointer to the map.

Just a few days ago I worked with one doing CreateDIBSection and figured out what that really means. Then yesterday I saw that I needed just that and and was able to create it.

Thank you for taking the time to reply.

[kooth]

You're most welcome bkelly! These pointer to pointer issues always seem to bite me. You'ed think I would have it down since I've been programming in C since 1986 and C++ since 1991. Sheesh!

Thank you for your patience with me!