Thread: STL - map

This code doesn´t work! The value of values[tempS] is always 0.
What is the problem??

Code:

#include <map.h>
#include <iostream.h>

int main(void){

  typedef std::map< char *, int, std::less<char *> > mapping;

  mapping values;

  values.insert( mapping::value_type("num1", 5 ));
  values.insert( mapping::value_type("num2", 15 ));

  char tempS[5];
  int tempI;

  cout << "Insert a string corresponding to a number:\n" ;
  cin.getline( tempS , 5 );
  cout << "Insert an int to be added:\n" ;
  cin >> tempI;

  cout << values[tempS] << " + " << tempI;
  tempI+=values[tempS];
  cout << " = " << tempI << endl;
  
  /*two cin.get to hold the screen, 
  don´t know better way*/
  cin.get(); 
  cin.get();
  
  return 0;
}

Code:

#include <iostream>	//remove .h
#include <map>
using namespace std;	//always usefull

int main()
{
      map< char*, int> values;	// sorry i dont know what is less so i just removed it..

      values["num1"] = 5;	//this is a better way to initialize values
      values["num2"] = 15;

      char tempS[5] = "null";//either use pointer or array not both or u will get an array of char pointer..
      int tempI = 0;

      cout << "Insert a string corresponding to a number:"<< endl ;
      cin >> tempS;	//i removed getline cause i didnt tought u needed it for a char array of
		    //only 5 char but u can always put it back..
      cout << "Insert an int to be added:"<< endl ;
      cin >> tempI;
      values[tempS] = tempI;	//thats why it always was 0 u forgot to put it in
      cout << values[tempS] << " + " << tempI;
      tempI+=values[tempS];
      cout << " = " << tempI << endl;
      return 0;
}

like i said i dunno what is less so could u explain it to me?

>like i said i dunno what is less so could u explain it to me?

I copied this code from C++ how to program, and I read that less<class T> would be used for sorting. You misunderstood the program(my fault, I didn´t explain nothing, sorry). But the user would input "num1" or "num2" to get a number from the map. This was a solution to another problem from this forum. Anyway, what return 0 in my original program is values["num1"].
I agree with your changes, and I tested your code, but I get the same error.
Here is my console window at the end of the program(just a note, I removed the line: values[tempS] = tempI, because I need the value stored before in the map)

Insert a string corresponding to a number:
num1
Insert an int to be added:
6
0 + 6 = 6

Now, why is that the line: values["num1"] = 5 have no effect here?

Thanks for the tips about my code!!

>> I removed the line: values[tempS] = tempI, because I need the value stored before in the map

If u remove that line u will always get 0 :

...

Code:

tempI+=values[tempS]

lets say tempI = 10 and tempS = "bob"

so ur trying to addition 10 plus the associated value of bob..

but since u never inserted bob in the map it will always return 0+10..

>> Now, why is that the line: values["num1"] = 5 have no effect here?

because ur not using it!
But if what u really want to do is add tempI to num1..
what u should do is :

Code:

      values[tempS] = tempI;
      cout << values[tempS] << " + " << tempI;
      values[num1]+=values[tempS];
      cout << " = " << tempI << endl;

but if u do not want to store tempS do like this:
(if ur not gonna store the value of tempS in the map why asking a name for it?)

Code:

      cout << values[tempS] << " + " << tempI;
      tempI+=values[num1];
      cout << " = " << tempI << endl;

unless I got what u really wanna do wrong once again..
hope that helped

opps i just red ur post again what u want to do is :
user input either num1 or num2 then a number to add to it?
if thats what u want second option should work..
but ill check it out just in case ill be back to u with an answer later..

Ok dont ask why but this will work..
If u replace cstring by c++ string all goes fine..
anyways i almost always use c++ string..

Code:

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main()
{
      map< string, int> values;
      values["num1"] = 5;
      values["num2"] = 15;

      char tempS[5];
      int tempI = 0;

      cout << "Insert a string corresponding to a number:"<< endl ;
      cin >> tempS;
      cout << "Insert an int to be added:"<< endl ;
      cin >> tempI;
      
      cout << values[tempS] << " + " << tempI << " = " << (tempI+=values[tempS]) << endl;
      return 0;
}

I´m so unhappy! None of the compilers that I have compiled the code.
Using Borland C++, I get an error message that says that map without that inspid less<T> have to few arguments. And putting less<string> I get another error: Illegal struct operation. Damn! I hate these compilers. Anyway, I have here posted the definition of my compiler´s code to the less struct(??):

Code:

template <class T>
struct less : public binary_function<T, T, bool>
{
    bool operator() (const T& x, const T& y) const { return x < y; }
};

As you can see, there is no reason to get any errors:
map< string, int, less <string> > values;
*sigh*... I thank your help! I´ll try to find another compiler to get this right...
Just for note, compiler are:
Turbo C++(in worst case)
Dev C++
Borland C++

If u use less only to sort values within the map its kinda useless.. cause:
values within maps and multimaps are already sorted smallest value first..
same for <set> and <multiset>..

But to insert an element in the correct position, you must search the right position, comparing the value to be inserted with the others that are already in the map/set. Correct? But good that you mentioned the fact that they are already sorted. I read this today, but forgot(incredible isn´t?).

Maps with char* as key won't work without a custom sorter because less<> only compares pointer values in this case. The std::string class however provides the < operator necessary for less<> to work properly.

The third template parameter to std::map is a function object type that is used for sorting the keys and deciding where to put them. The parameter should default to less<>, so if the borland compiler complains about too few parameters it's probably a compiler or std library bug.

If less<string> doesn't work it's probably a bug too.