C / C++ / MFC

30-Jul-02 2:49

I'm having a strange problem with the STL map.find(). I have a function which I search for an item's existance with a find() before inserting. If I don't find it, I insert it. Trouble is, when an item already exists in the map, both the find() and count() never report it. Also, the insert() lets me add a duplicate key. Below find declarations, code, and debug output.

// declarations
typedef struct ImportDataType
{
CString Item;
CString Value;
char Type;
long ReplicationID;
} ImportDataType;

typedef vector<importdatatype> dataVector;
typedef map<const char="" *,="" datavector=""> importData;

map<const char="" *,="" dataimportdata::datavector="">::const_iterator mapIter;

int i = dataMap.count(m_currentEID);
int j = dataMap.size();

TRACE ("\nIn AddDataItem, b4 map.insert(), size of Map = %d\n",j);
TRACE ("Number of items in the Map with key of %s = %d\n",m_currentEID,i);

mapIter = dataMap.find(m_currentEID);

if (mapIter != dataMap.end())
TRACE ("B4 insert, key found in map!\n");
else
TRACE ("B4 insert, key not found in map!\n");

for (mapIter = dataMap.begin();
mapIter != dataMap.end(); mapIter++)
{
TRACE ("Key from Map = %s\n", (*mapIter).first);
}

dataMap.insert(make_pair(m_currentEID, dataVector));
mapIter = dataMap.find(m_currentEID);

if (mapIter != dataMap.end())
TRACE ("After insert, found key in map!\n");
else
TRACE ("After insert, key not found in map!\n");

i = dataMap.count(m_currentEID);
j = dataMap.size();

TRACE ("\nIn AddDataItem, after map.insert(), size of Map = %d\n",j);
TRACE ("Number of items in the Map with key of %s = %d\n",m_currentEID,i);

for (mapIter = dataMap.begin();
mapIter != dataMap.end(); mapIter++)
{
TRACE ("Key from Map = %s\n", (*mapIter).first);
}

The partial output from running this shows the problem. Note the key values are being printed before the insert is done. The key 6748 does exist, but the map.count() and map.find() are not reporting it. Note in the last dump of the map keys that 6748 is there twice! What am I doing wrong?

In AddDataItem, b4 map.insert(), size of Map = 3
Number of items in the Map with key of 982000006006748 = 0
B4 insert, key not found in map!
Key from Map = 982000006003798
Key from Map = 982000007172537
Key from Map = 982000006006748
After insert, found key in map!

In AddDataItem, after map.insert(), size of Map = 4
Number of items in the Map with key of 982000006006748 = 1
Key from Map = 982000006003798
Key from Map = 982000007172537
Key from Map = 982000006006748
Key from Map = 982000006006748

Any ideas are appreciated as to why this does not work!
Thanks in advance,
Bob

Alexandru Savescu30-Jul-02 3:09

30-Jul-02 3:09

There is something wrong with your code. How do you sort your items? You have to provide a < operator so the map can insert and lookup your items. And also, please format your code and change < and > with &lt and > so we can see your code better.

Best regards,
Alexandru Savescu

moobob30-Jul-02 3:25

30-Jul-02 3:25

Alex,

Thanks for your response, sorry, I don't know how to format my code for the post, can you please tell me how? Since I don't provide a sorting criterion when I define my map, it should use the default less <>? I don't really understand the sorting criterion very well. I can see my items don't appear to be sorted. All I want to do is insert items and find items. How should I specify it?

thanks,
Bob

Alexandru Savescu30-Jul-02 3:31

30-Jul-02 3:31

Use the <pre> tags. You can use them on the formatting bar just above the smileys. Also you can preview the messge before it gets posted.

In a map items will be sorted by key. If you use int as keys then you need not provide a < operator. But if your are using some structs then you definitely must give a comparison method.

Best regards,
Alexandru Savescu

moobob30-Jul-02 3:36

30-Jul-02 3:36

I am using a key of const char *, the data is struct. How would I specify a comparison method for char *?

thanks,
Bob

Alexandru Savescu30-Jul-02 3:37

30-Jul-02 3:37

Taking a closer look the HTML source page I found this

typedef map<const char *, dataVector> importData;

So you are using some const char* as string. Using less on them will compare pointers and of course that your map will not look as you expect. You must compare them with strcmp. Or, easier use CString as key. It has a < operator defined that does good job.

Best regards,
Alexandru Savescu

moobob30-Jul-02 3:45

30-Jul-02 3:45

Alex,

Making the key a CString worked!!! Thank you very much for your help!

Bob

Alexandru Savescu30-Jul-02 3:55