c++ transform with pair go in Segmentation fault

Question

This code works:

class Test
{
public:
  Test(string name) : _name(name) {};
  bool operator()() { cout << "hello " << _name << endl; return true; }
  string name() { return _name; }
private:
  string _name;
};

pair<string, bool>
inline execute_test(Test* t) {
  return pair<string, bool>(t->name(), (*t)());
}

int main()
{
  vector<Test*> tests;
  vector<pair<string, bool> > results;
  tests.push_back(new Test("Test1"));
  tests.push_back(new Test("Test2"));

  for (unsigned int i=0; i < tests.size(); ++i)
      results.push_back(execute_test(tests[i]));

}

now I want to use trasform instead of the for cicle:

transform(tests.begin(), tests.end(),
          results.begin(),
          execute_test);

but I got a Segmentation Fault. Where is the problem?

Answer 1

That is because transform is expecting results object to have the required memory allocated i.e. it is expecting results.size() is atleast as big as tests.size(). If you want to push_back operation to be performed on the results then you should use std::back_inserter(results) as the third argument. Otherwise, when transform uses the * output iterator you passed, it will be a invalid memory location and will result in a segmentation fault.