Is `sizeof` in C Evaluated at Compile Time or Runtime?

Evaluating sizeof in C : Compile Time or Runtime?

In C , sizeof is an operator that returns the size of a data type or variable in bytes. Understanding when sizeof is evaluated is crucial for optimizing code efficiency.

Compilation Time vs. Runtime

The evaluation of sizeof differs depending on whether it is being used at compilation time or runtime.

At compilation time, sizeof is evaluated. The compiler determines the size of the data type or variable based on the machine architecture it is being compiled for. For example, sizeof(short int) will typically return 2 bytes on 32-bit machines and 4 bytes on 64-bit machines.

However, at runtime, the size of a data type or variable may change dynamically. For instance, in embedded systems, the data type size may vary depending on the underlying microcontroller architecture. In such scenarios, using sizeof at runtime would result in inaccurate values.

Code Snippet Explanation

In the provided code snippet:

<code class="c++">sizeof(short int)</code>

The sizeof operator evaluates the size of the short int data type at compilation time. It returns the size in bytes, which depends on the compiler machine architecture. Therefore, the result of this code snippet will be determined by the machine on which the compiler is running, not the machine on which the executable file is运行。

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