sizeof operator

Queries size of the object or type.

Used when actual size of the object must be known.

Syntax

Both versions return a value of type size_t.

Explanation

Notes

Depending on the computer architecture, a byte may consist of 8 or more bits, the exact number provided as CHAR_BIT

sizeof(char), sizeof(signed char), and sizeof(unsigned char) always return 1

sizeof cannot be used with function types, incomplete types (including void), or bit-field

When applied to an operand that has structure or union sizeof(T) returns the size of an element of a T[]

Except if the type of expression is a VLA,(since C99) expression is not evaluated and the sizeof operator may be used in an integer constant expression

Number of elements in any array a including VLA(since C99) may be determined with the expression sizeof a / sizeof a[0] . Note that if a

Keywords

sizeof

Example

#include <stdio.h>
 
int main(void)
{
    short x;
    // type argument:
    printf("sizeof(float)          = %zu\n", sizeof(float));
    printf("sizeof(void(*)(void))  = %zu\n", sizeof(void(*)(void)));
    printf("sizeof(char[10])       = %zu\n", sizeof(char[10]));
//  printf("sizeof(void(void))     = %zu\n", sizeof(void(void))); // Error: function type
//  printf("sizeof(char[])         = %zu\n", sizeof(char[])); // Error: incomplete type
 
    // expression argument:
    printf("sizeof 'a'             = %zu\n", sizeof 'a'); // type of 'a' is int
//  printf("sizeof main            = %zu\n", sizeof main); // Error: Function type
    printf("sizeof &main           = %zu\n", sizeof &main);
    printf("sizeof \"hello\"         = %zu\n", sizeof "hello"); // type is char[6]
    printf("sizeof x               = %zu\n", sizeof x); // type of x is short
    printf("sizeof (x+1)           = %zu\n", sizeof(x + 1)); // type of x+1 is int
}

sizeof(float)          = 4
sizeof(void(*)(void))  = 8
sizeof(char[10])       = 10
sizeof 'a'             = 4
sizeof &main           = 8
sizeof "hello"         = 6
sizeof x               = 2
sizeof (x+1)           = 4

References

See also