Difference between sizeof(struct structname) and sizeof(object) in C

Question

Are there scenarios where there can be a difference between sizeof(struct structure_name) and sizeof(object) where object is of type struct structure_name in C?

Answer 1

No there is no difference between sizeof(type) and sizeof(o) where the declared type of o is type.

There can be differences if the declared type of the object isn't truly representative of the object. For example

char arrayValue[100];
sizeof(arrayValue);  // 100 on most systems
char* pointerValue = arrayValue;
sizeof(pointerValue);  // 4 on most 32 bit systems

This difference occurs because sizeof is a compile time construct in C. Hence there is no runtime analysis and the compiler looks instead at the statically declared types.