size_t - cppreference.com (original) (raw)
| Defined in header <stddef.h> | | | | ----------------------------------------------------------------------- | ----------- | | | Defined in header <stdio.h> | | | | Defined in header <stdlib.h> | | | | Defined in header <string.h> | | | | Defined in header <time.h> | | | | Defined in header <uchar.h> | (since C11) | | | Defined in header <wchar.h> | (since C95) | | | typedef /*implementation-defined*/ size_t; | | |
size_t is the unsigned integer type of the result of sizeof, offsetof and _Alignof(until C23)alignof(since C23), depending on the data model.
| The bit width of size_t is not less than 16. | (since C99) |
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[edit] Notes
size_t can store the maximum size of a theoretically possible object of any type (including array).
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.
| Possible implementation typedef typeof(sizeof(0)) size_t; | (since C23) |
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[edit] Example
#include <stddef.h> #include <stdint.h> #include <stdio.h> int main(void) { const size_t N = 101; int numbers[N]; size_t sum = 0; for (size_t ndx = 0; ndx < N; ++ndx) sum += numbers[ndx] = ndx; size_t size = sizeof numbers; printf("sum = %zu\n", sum); printf("size = %zu\n", size); printf("SIZE_MAX = %zu\n", SIZE_MAX); }
Possible output:
sum = 5050 size = 404 SIZE_MAX = 18446744073709551615
[edit] References
C23 standard (ISO/IEC 9899:2024):
7.19 Common definitions <stddef.h> (p: TBD)
7.20.3 Limits of other integer types (p: TBD)
C17 standard (ISO/IEC 9899:2018):
7.19 Common definitions <stddef.h> (p: 211)
7.20.3 Limits of other integer types (p: 215)
C11 standard (ISO/IEC 9899:2011):
7.19 Common definitions <stddef.h> (p: 288)
7.20.3 Limits of other integer types (p: 293)
C99 standard (ISO/IEC 9899:1999):
7.17 Common definitions <stddef.h> (p: 253)
7.18.3 Limits of other integer types (p: 258)
C89/C90 standard (ISO/IEC 9899:1990):
4.1.6 Common definitions <stddef.h>