What is the difference between the front() and begin() functions that appears in many STL containers?
5 Answers
begin() returns an iterator that can be used to iterate through the collection, while front() just returns a reference to the first element of the collection.
answered Feb 15, 2012 at 23:24
Joachim Isaksson
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1 Comment
David Rodríguez - dribeas
+1 Just to make things more explicit (or maybe complicate):
&c.front() == &*c.begin() for any container that has at least one element. Comparing the address-of the expressions is used to demonstrate that it is not the values that are the same, but the objects (i.e. c.front() yields a reference to the same object that dereferencing the begin iterator *c.begin()).front() returns a reference to the first element, begin() returns an iterator to it.
Note that you shouldn't call front on an empty container, but it's OK to call begin as long as you don't dereference the iterator that begin returns.
Comments
The front member returns a reference to the first member of a list or vector. The begin function returns an iterator (which is more like a pointer) initialized to the first member of a list, map, or vector.
Comments
From http://www.cplusplus.com/reference/stl/vector/begin/ (literally the first google result for "vector::begin"):
Notice that unlike member
vector::front, which returns a reference to the first element, this function returns a random access iterator.
Comments
front()
- Returns a reference to the first element of the array
- Provides direct access to the first element.
- Can modify the first element alone
begin()
- Returns an iterator pointing to the first element of the array.
- It is used to iterate over the array or access elements using iterator operations.
- Can modify elements through iteration
front()is identical to*begin().