Vector insert() causes program to crash

Question

This is the first part of a function I have that's causing my program to crash:

vector<Student> sortGPA(vector<Student> student) {
    vector<Student> sorted;
    Student test = student[0];
    cout << "here\n";
    sorted.insert(student.begin(), student[0]);
    cout << "it failed.\n";
         ...

It crashes right at the sorted part because I can see "here" on the screen but not "it failed." The following error message comes up:

Debug Assertion Failed!

(a long path here...)

Expression: vector emplace iterator outside range

For more information on how your program can cause an assertion
failure, see the Visual C++ documentation on asserts.

I'm not sure what's causing the problem now, since I have a similar line of code elsewhere student.insert(student.begin() + position(temp, student), temp); that does not crash (where position returns an int and temp is another declaration of a struct Student). What can I do to resolve the problem, and how is the first insert different from the second one?

Answer 1

It should be:

sorted.insert(sorted.begin(), student[0]);

You were passing the iterator from the wrong instance.

Answer 2

When you use std::vector::insert ( iterator position, const T& x );, the iterator position must point into that same vector. You're using an iterator from student with sorted.insert, which dies.