What does the `sizeof` operator do in C?

The sizeof operator in C is used to determine the size, in bytes, of a specified data type or object. When you apply sizeof to a data type, such as int, char, or float, it returns the number of bytes that type occupies in memory. For example, using sizeof(int) typically evaluates to 4 on many systems, indicating that an integer occupies 4 bytes of memory.

Additionally, when sizeof is applied to a variable, it provides the size of the variable's type. This is particularly useful for dynamic memory management, ensuring that enough space is allocated for different data types. The operator is evaluated at compile time, which enhances performance and provides safety by allowing developers to understand memory requirements better.

The other choices do not accurately describe the function of the sizeof operator. For instance, returning the length of a string is typically done using functions like strlen, while counting the number of elements in an array requires knowledge of the total size of the array divided by the size of a single element. Memory allocation for a variable is performed through functions like malloc or calloc, not the sizeof operator.