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sizeof()

Last revision 05/14/2024

Description

The 

sizeof
operator returns the number of bytes in a variable type, or the number of bytes occupied by an array.

Syntax

sizeof(variable)

Parameters

variable
: The thing to get the size of. Allowed data types: any variable type or array (e.g. 
int
, 
float
, 
byte
).

Returns

The number of bytes in a variable or bytes occupied in an array. Data type: 

size_t
.

Example Code

The 

sizeof
operator is useful for dealing with arrays (such as strings) where it is convenient to be able to change the size of the array without breaking other parts of the program.

This program prints out a text string one character at a time. Try changing the text phrase.

1char myStr[] = "this is a test";
2

3    void setup() {
4      Serial.begin(9600);
5    }
6

7    void loop() {
8      for (byte i = 0; i < sizeof(myStr) - 1; i++) {
9        Serial.print(i, DEC);
10        Serial.print(" = ");
11        Serial.write(myStr[i]);
12        Serial.println();
13      }
14      delay(5000);  // slow down the program
15    }

Notes and Warnings

Note that 

sizeof
returns the total number of bytes. So for arrays of larger variable types such as 
int
s, the for loop would look something like this.

1int myValues[] = {123, 456, 789};
2

3    // this for loop works correctly with an array of any type or size
4    for (byte i = 0; i < (sizeof(myValues) / sizeof(myValues[0])); i++) {
5      // do something with myValues[i]
6    }

Note that a properly formatted string ends with the NULL symbol, which has ASCII value 0.

See also

Suggest changes

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The Arduino documentation is licensed under the Creative Commons Attribution-Share Alike 4.0 license.

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