How to Get the Size of Array in C

  1. sizeof() Operator to Determine the Size of an Array in C
  2. Get Length of Array in C

This tutorial introduces how to determine the length of an array in C. The sizeof() operator is used to get the size/length of an array.

sizeof() Operator to Determine the Size of an Array in C

The sizeof() operator is a compile-time unary operator. It is used to calculate the size of its operand. It returns the size of a variable. The sizeof() operator gives the size in the form of a byte.

The sizeof() operator is used for any data type such as primitives like int, float, char, and also non-primitives data type as an array, struct. It returns the memory allocated to that data type.

The output may be different on different machines like a 32-bit system can show different output and a 64-bit system can show different of the same data types.

Syntax of sizeof():

sizeof(operand)
  • The operand is a data-type or any operand.

sizeof() Operator for Primitive Data Types in C

This program uses an int, float as a primitive data type.

#include <stdio.h> 

int main(void) 
{ 
    printf("Size of char data type: %u\n",sizeof(char)); 
    printf("Size of int data type: %u\n",sizeof(int)); 
    printf("Size of float data type: %u\n",sizeof(float)); 
    printf("Size of double data type: %u\n",sizeof(double)); 
    
    return 0; 
}

Output:

Size of char data type: 1
Size of int data type: 4
Size of float data type: 4
Size of double data type: 8

Get Length of Array in C

If we divide the array’s total size by the size of the array element, we get the number of elements in the array. The program is as below:

#include<stdio.h>

int main(void) 
{
    int number[16];
    
    size_t n = sizeof(number)/sizeof(number[0]);
    printf("Total elements the array can hold is: %d\n",n);
    
    return 0;
}

Output:

Total elements the array can hold is: 16

When an array is sent as a parameter to the function, it treats as a pointer. The sizeof() operator returns the pointer size instead of array size. So inside functions, this method won’t work. Instead, pass an additional parameter size_t size to indicate the number of elements in the array.

#include<stdio.h>
#include<stdlib.h>

void printSizeOfIntArray(int intArray[]);
void printLengthIntArray(int intArray[]);

int main(int argc, char* argv[])
{
    int integerArray[] = { 0, 1, 2, 3, 4, 5, 6 };

    printf("sizeof of the array is: %d\n", (int) sizeof(integerArray));
    printSizeOfIntArray(integerArray);
    
    printf("Length of the array is: %d\n", (int)( sizeof(integerArray) / sizeof(integerArray[0]) ));
    printLengthIntArray(integerArray);

}

void printSizeOfIntArray(int intArray[])
{
    printf("sizeof of the parameter is: %d\n", (int) sizeof(intArray));
}

void printLengthIntArray(int intArray[])
{
    printf("Length of the parameter is: %d\n", (int)( sizeof(intArray) / sizeof(intArray[0]) ));
}

Output (in a 64-bit Linux OS):

sizeof of the array is: 28
sizeof of the parameter is: 8
Length of the array is: 7
Length of the parameter is: 2

Output (in a 32-bit Windows OS):

sizeof of the array is: 28
sizeof of the parameter is: 4
Length of the array is: 7
Length of the parameter is: 1
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