Defined in header <cstddef> | ||
---|---|---|
Defined in header <cstdio> | ||
Defined in header <cstring> | ||
Defined in header <ctime> | ||
Defined in header <cstdlib> | (since C++11) | |
Defined in header <cwchar> | (since C++11) | |
typedef /*implementation-defined*/ size_t; |
std::size_t
is the unsigned integer type of the result of the sizeof
operator as well as the sizeof...
operator and the alignof
operator (since C++11).
Notes
std::size_t
can store the maximum size of a theoretically possible object of any type (including array). A type whose size cannot be represented by std::size_t
is ill-formed (since C++14) On many platforms (an exception is systems with segmented addressing) std::size_t
can safely store the value of any non-member pointer, in which case it is synonymous with std::uintptr_t
.
std::size_t
is commonly used for array indexing and loop counting. Programs that use other types, such as unsigned int
, for array indexing may fail on, e.g. 64-bit systems when the index exceeds UINT_MAX
or if it relies on 32-bit modular arithmetic.
When indexing C++ containers, such as std::string
, std::vector
, etc, the appropriate type is the member typedef size_type
provided by such containers. It is usually defined as a synonym for std::size_t
.
Example
#include <cstddef> #include <iostream> int main() { const std::size_t N = 10; int* a = new int[N]; for (std::size_t n = 0; n < N; ++n) a[n] = n; for (std::size_t n = N; n-- > 0;) // Reverse cycles are tricky for unsigned types. std::cout << a[n] << " "; delete[] a; }
Output:
9 8 7 6 5 4 3 2 1 0
See also
signed integer type returned when subtracting two pointers (typedef) | |
byte offset from the beginning of a standard-layout type to specified member (function macro) | |
C documentation for size_t |
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