Example
A unary operator that yields the size in bytes of its operand, which may be either an expression or a type. If the operand is an expression, it is not evaluated. The size is a constant expression of type std::size_t.
If the operand is a type, it must be parenthesized.
- It is illegal to apply
sizeofto a function type. - It is illegal to apply
sizeofto an incomplete type, includingvoid. - If sizeof is applied to a reference type
T&orT&&, it is equivalent tosizeof(T). - When
sizeofis applied to a class type, it yields the number of bytes in a complete object of that type, including any padding bytes in the middle or at the end. Therefore, asizeofexpression can never have a value of 0. See layout of object types for more details. - The
char,signed char, andunsigned chartypes have a size of 1. Conversely, a byte is defined to be the amount of memory required to store acharobject. It does not necessarily mean 8 bits, as some systems havecharobjects longer than 8 bits.
If expr is an expression, sizeof(expr) is equivalent to sizeof(T) where T is the type of expr.
int a[100];
std::cout << "The number of bytes in `a` is: " << sizeof a;
memset(a, 0, sizeof a); // zeroes out the array
C++11
The sizeof... operator yields the number of elements in a parameter pack.
template <class... T>
void f(T&&...) {
std::cout << "f was called with " << sizeof...(T) << " arguments\n";
}
