In the C++ Primer
book, Chapter (3), there is the following for-loop that resets the elements in the vector to zero.
for (vector<int>::size_type ix = 0; ix ! = ivec.size(); ++ix)
ivec[ix] = 0;
Why is it using vector<int>::size_type ix = 0
? Cannot we say int ix = 0
? What is the benefit of using the first form on the the second?
Thanks.
The C++ Standard says,
size_type | unsigned integral type | a type that can represent the size of the largest object in the allocation model
Then it adds,
Implementations of containers described in this International Standard are permitted to assume that their Allocator template parameter meets the following two additional requirements beyond those in Table 32.
- The typedef members pointer, const_pointer, size_type, and difference_type are required to be T*,T const*, size_t, and ptrdiff_t, respectively
So most likely, size_type
is a typedef of size_t
.
And the Standard really defines it as,
template <class T>
class allocator
{
public:
typedef size_t size_type;
//.......
};
So the most important points to be noted are :
size_type
is unsigned
integral, while int
is not necessarily unsigned
. :-)