Re: initialize reference

"kanze" <>
25 Jul 2006 07:56:34 -0400
jean wrote:

I have the following code. Basically, I want to insert to
different map depends on m_bDefaultTag . I know I need to
initialize updateTags. But how? Is there a way to achieve my
goal? Thanks.

class tag_entry
string m_name;
int value;

void MyFunc()
            std::map<std::string, tag_entry >& customTags =
            std::map<std::string, tag_entry >& defineTags =
            std::map<std::string, tag_entry >& updateTags;

            if( m_bDefaultTag ) {
                  updateTags = defineTags;
            else {
                  updateTags = customTags;

    std::map< std::string, tag_entry >& updateTags
        = m_bDefaultTag ? GetDefineTags() : GetCustomTags() ;

            customTags.insert( mapElement );

In more complicated cases, you use pointers. If you really need
a reference, you then initialize the reference by dereferencing
the pointers. Something like:

    Map* customTags = GetCustomTags() ;
    Map* defineTags = GetDefineTags() ;
    Map* pUpdateTags = NULL ;
    if ( m_bDefaultTag ) {
        pUpdateTags = defineTags ;
    } else {
        pUpdateTags = customTags ;
    Map& updateTags = *pUpdateTags ;

(Obviously, in such a simple case, you'd use the conditional
expression to initialize pUpdateTags, and only call
GetCustomTags() or GetDefineTags() as necessary. Which means
you end up with my first suggestion. But on a few occasions,
I've had to deal with much more complicated decision structures,
and using pointer, as here, has been necessary.)

James Kanze GABI Software
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