Problem in Map Count MEthod

**nickman** · 09-10-2016

Hi All

I am trying to insert values in map as <char*,int> .

The key is combination of 2 numbers which is generated in code.

The problem is when I am trying to get count of that key, it is giving me 0.

Below is sample code.

Code:

#include <iostream>
#include <map>

using namespace std;

int main ()
{
  std::map<char*,int> mp;
  char key[10] = {0x00};

  char mapKey[10] = {0x00};

  sprintf(key,"%d%d",0,0);

 mp.insert(std::pair<char*,int>(key,4));

 sprintf(mapKey,"%d%d",0,0);

  int count = mp.count(mapKey); 

  if ( count > 0 )
	  cout<<"\n Key Found";
  else
	  cout <<"\n Not found\n";


  std::map<char*,int>::iterator it;

// This is printing correct values of map

  for (it=mp.begin(); it!=mp.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';


  getchar();
}

OutPut: Not Found
00=> 4
So map has value but count() is failing.
Can any body help me here.

Thanks
Bhagwat

**Prelude** · 09-10-2016

Your key is compared as a pointer, not a string. Unless it's the same pointer used for count as was inserted, the lookup will fail. You could add a comparison delegate to make things work, but it would be better in general to stick with the std::string class instead of using C-style strings:

Code:

#include <iostream>
#include <map>
#include <string>

using namespace std;

int main()
{
	map<string, int> mp;
	string key = to_string(0) + to_string(1);

	mp[key] = 4;

	cout << "Key" << (mp.count("01") != 0 ? " found" : "not found") << '\n';

	for (auto it : mp)
	{
		cout << it.first << " => " << it.second << '\n';
	}
}

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