problem with map

[Mohammad Mahmudur Rahman]

Hi,
The STL Map is driving me mad.
Can someone tell me why the following program -

Code: Select all

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

struct ltstr
{
	bool operator()(const char *s1, const char *s2) const
	{
		return (strcmp(s1,s2)<0);
	}
};

int main(void)
{
	int i;
	char buf[100];
	map<const char *,int,ltstr> mp;

	for(i=0;i<5;i++)
	{
		cin>>buf;
		mp[buf] = i + 1;
	}

	for(i=0;i<5;i++)
	{
		cin>>buf;
		if(mp.find(buf)!=mp.end())
			cout<<mp[buf]<<endl;
	}

	return 0;
}//end main()

should produce -

Code: Select all

5
5
5
5
5

instead of -

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1
2
3
4
5

[Krzysztof Duleba]

buf is just a memory address. It stays the same in each iteration of your loop. You should use strings instead or create a new buffer for each input string (which is a bad idea as you're not familiar with pointers).

[Mohammad Mahmudur Rahman]

Thanks for your reply. As I am not very accustomed with the use of STL, I was almost certain that there's something wrong with my STL structure & in the process, forgot the basic pointer behaviour. Thanks again for pointing it out.