How to insert data in a nested STL map ?

Aquarius_Girl · 12-13-2010, 06:07 AM

Following is the declaration:

Code:

std :: map <QString, std :: vector <std :: pair <QString, QString> > > configFileDataVector;

How should I insert data in it?
All the examples which I have looked up in Google are of plain maps!!

I need help!

I tried this, but it failed:

Code:

configFileDataVector.insert (pair <QString, std :: vector <std :: pair <QString, QString> > > ("df", ("1","4")));

and also tried this:

Code:

configFileDataVector.insert (std::make_pair ("fdsf", ("Peter Q.","5328")));

It shows a warning:

Quote:

left-hand operand of comma has no effect

tuxdev · 12-13-2010, 12:54 PM

There's no point getting tricky with this, it just makes for confusing syntax when you try:

Code:

configFileDataVector["fdsf"].push_back(std::pair<QString, QString>("Peter Q.","5328"));

Aquarius_Girl · 12-15-2010, 02:23 AM

Thanks for bothering

The following made it work and you also wrote the similar thing, and I admit that I didn't put much brains into it, I shall think harder next time!

I have shown the relevant code here, it might be helpful to someone else.

Code:

std :: map <QString, std :: vector <std :: pair <QString, QString> > > configFileDataVector;
std :: map <QString, std :: vector <std :: pair <QString, QString> > > :: iterator mapIterator;

for (mapIterator = configFileDataVector.begin(); mapIterator != configFileDataVector.end(); ++mapIterator)
{
   if ((*mapIterator).first == openingTagName)
   {
      configFileDataVector[openingTagName].push_back (std :: make_pair (objQXmlReader.name().toString(), objQXmlReader.readElementText ()));
      break;
    }
}

Aquarius_Girl · 03-02-2011, 01:43 AM

I am not able to figure out these simple issues on my own

Feel free to throw bricks and bats at me!

The map has been declared as:

Code:

std :: map <unsigned int, char[4111]> dataReceivedFromComponents;

I am filling in the data as:

Code:

char temp [4111];
memcpy (temp, receivedData, (dataSize + 16));
dataReceivedFromComponents [0] = temp;

and getting the error:

Quote:

error: invalid array assignment

HELP!

dwhitney67 · 03-02-2011, 04:15 AM

I don't have much time to explain, but take a look at the following; it will probably simplify your code:

Code:

#include <string>
#include <map>

using namespace std;

int main()
{
   typedef basic_string<char> ComponentData;
   map<int, ComponentData>    dataRcvdFromComponent;

   char   receivedData[4011] = {0};  // data from your component; for now, all zeroes
   size_t dataSize = 3456 + 16;      // number of bytes received from the component; not sure where the 16 comes from?

   dataRcvdFromComponent.insert(make_pair(0, ComponentData(receivedData, dataSize)));

   // or the less efficient, but easier to read

   dataRcvdFromComponent[0] = ComponentData(receivedData, dataSize);
}

--------------
EDIT:

Now that I have the time, what I wanted to indicate earlier is that the "value" type of your STL map needs to be copyable, and that a char array does not offer that feature. In other words, in regular C or C++, this would not work:

Code:

char a[4111];
char b[4111];

b = a;   // error: ISO C++ forbids assignment of arrays

P.S. If your component data is a collection of unsigned bytes, then use "unsigned char" in lieu of "char" above; or better yet, use "uint8_t".