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

sizeof()Operator determines the size of an array in C

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

sizeof()The operator is used for any data type, primitives like int, float, etc. and also for non-primitive data types like , . It returns the memory allocated for that data type .chararraystruct

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.

sizeof()Syntax

sizeof(operand)

• operandis a data type or any operand.

sizeof()Operands for primitive data types in C

This program uses int, floatas primitive data types.

#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 the length of an array in C

If we divide the total size of the array by the size of the array element, we can get the number of elements in the array. The procedure is as follows.

#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 passed as a parameter to a function, it is treated as a pointer. sizeof()The operator returns the pointer size, not the array size. So inside a function, this method does not work. Instead, pass an additional parameter size_t sizeindicating 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 (on a 64-bit Linux operating system):

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 (on 32-bit Windows operating systems):

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