std::map declared in header is null?

[BlueGhost79]

Hi,
I declare a std::map in my header file, but when I go to add an item to it in the class it crashes as it is null.


header file

class x
{
public:
void DoStuff();
private:
std::map<int, int> sample_data;

};


source file

void DoStuff()
{
//crashes here as sample_data is null
sample_data[4] = 5;
}


why would the sample_data variable be null?

void DoStuff()
{
//crashes here as sample_data is null
std::map<int, int> sample_data;
sample_data[4] = 5;
}

will work, if sample_data is a local variable.

 

[2ffat]

Just a thought as I haven't looked too closely. If it works for a local variable, shouldn't you call the class x's sample_data, something like x.sample_data[4] = 5? Also have you looked at using insert instead instead of assigning?


James P. Cottingham
-----------------------------------------
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[ArkM]

You have an empty map. No pair <int,int> with key 4 in the map! You assign a value to unexistent object.
You must insert element before access it. For example:

std::map<int,int> sample_data;
typedef std::pair<int,int> V;
...
sample_data.insert(V(4,4));
// Now you can access map element with key 4...
m[4] = 5; // or what else...