C The sizeof Operator
Get the Memory Size
We introduced in the data types chapter that the memory size of a variable varies depending on the type:
| Data Type | Size |
|---|---|
int |
2 or 4 bytes |
float |
4 bytes |
double |
8 bytes |
char |
1 byte |
The memory size refers to how much space a type occupies in the computer's memory.
To actually get the size (in bytes) of a data type or variable, use the sizeof operator:
Example
int myInt;
float myFloat;
double myDouble;
char myChar;
printf("%zu\n", sizeof(myInt));
printf("%zu\n", sizeof(myFloat));
printf("%zu\n", sizeof(myDouble));
printf("%zu\n", sizeof(myChar));
Try it Yourself »
Note that we use the %zu format specifier to print the result, instead of %d. This is because the compiler expects the sizeof operator to return a value of type size_t, which is an unsigned integer type. On some computers it might work with %d, but it is safer and more portable to use %zu, which is specifically designed for printing size_t values.
Why Should I Know the Size of Data Types?
Knowing the size of different data types is important because it says something about memory usage and performance.
For example, the size of a char type is 1 byte. Which means if you have an array of 1000 char values, it will occupy 1000 bytes (1 KB) of memory.
Using the right data type for the right purpose will save memory and improve the performance of your program.
You will learn more about the sizeof operator later in this tutorial, and how to use it in different scenarios.
