devxlogo

The Perils of a Container’s Reallocation

The Perils of a Container’s Reallocation

When a container reallocates its elements, their addresses change correspondingly. Consequently, the values of existing iterators are invalidated:

 #include #include using namespace std;void main() {  list  payroll;   payroll.push_back(5000.00);  list::iterator p = payroll.begin(); //p points to the first element  for (int i = 0 ; i < 10; i++) {      payroll.push_back(4500.00); //insert 10 more elements to payroll; reallocation may occur  }      // DANGEROUS  cout << "first element in payroll: "<< *p <

In this example, it may well be the case that payroll reallocated itself during the insertion of 10 additional elements, and as a result invalidated the value of p. Using an invalid iterator yields undefined behavior. It's exactly as if you were using a pointer with the address of a deleted object. To be on the safe side, you should re-assign the iterator's value:

 for (int i = 0 ; i < 10; i++) {  payroll.push_back(4500.00); //insert 10 more elements to payroll; reallocation may occur}   p = payroll.begin(); // re-assign p   cout <<"first element in payroll: "<<*p<
devxblackblue

About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

About Our Journalist