STL add comments to sort_until.

Author: cgyurgyik

STL_examples.cpp

@@ -566,12 +566,13 @@ TEST(sort, ExampleTwoWithPredicate) {
 TEST(is_sorted_until, ExampleOne) {
  std::vector<int> v{1, 2, 3, 4, 3, 5, 6};
  const auto iterator1 = std::is_sorted_until(v.cbegin(), v.cend());
+ // Points to the last sorted element.
  EXPECT_EQ(*iterator1, 3);
  EXPECT_EQ(iterator1 - v.cbegin(), 4);
 
  std::sort(v.begin(), v.end());
  const auto iterator2 = std::is_sorted_until(v.cbegin(), v.cend());
- EXPECT_EQ(iterator2, v.cend());
+ EXPECT_EQ(iterator2, v.cend()); // All elements are sorted.
  EXPECT_EQ(iterator2 - v.cbegin(), 7);
 }