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      size_t

      From cppreference.com
      <c‎ |types
       
       
       
      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 ofsizeof,offsetof and_Alignof(until C23)alignof(since C23), depending on thedata model.

      The bit width ofsize_t is not less than 16.

      		(since C99)

      Contents

      [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 asunsignedint, for array indexing may fail on, e.g. 64-bit systems when the index exceedsUINT_MAX or if it relies on 32-bit modular arithmetic.

      Possible implementation

      typedef typeof(sizeof(0)) size_t;

      		(since C23)

      [edit]Example

      Run this code
      #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 = 5050size = 404SIZE_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>

      [edit]See also

      signed integer type returned when subtracting two pointers
      (typedef)[edit]
      byte offset from the beginning of a struct type to specified member
      (function macro)[edit]
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