Question

I have defined a vector like this in the header file

class entry
{
   public: 
     int key;
     int next;
};
std::vector<entry *> TB;

in the cpp file, I wrote:

int s1, val;
s1 = 10; val = 2;
gh = (TB.size() % s1);

However when I want to write something to it, I get segmentation fault

TB[gh]->key = val;   

What is the problem with the assignment?

Answer 1

The vector has no elements. Use push_back() or insert() to add elements to the vector:

entry* e = new entry();
e->key   = val;
e->next  = 0;

TB.push_back(e);          // Append to vector.
TB.insert(TB.begin(), e); // Insert at beginning of the vector.

When destroying the vector TB you must iterate over the elements and delete each individually (or use a smart pointer as the element type, such as boost::shared_ptr<entry> or std::unique_ptr<entry>).

You could provide a constructor(s) for entry to make the addition of an entry to TB more concise:

class entry
{
public: 
    entry(int a_key, int a_next = 0) : key(a_key), next(a_next) {}
    int key;
    int next;
};

TB.push_back(new entry(val));
TB.insert(TB.begin(), new entry(val));