Why is `sizeof(void)` invalid in C, but evaluates to 1 in GCC?

Understanding the Size of Void

In C programming, the keyword void signifies a data type that has no size. This peculiar property makes it ineligible for variable declarations or memory allocation tasks.

Compilation Error: Void Pointer Allocation

The code snippet you provided:

void *p = malloc(sizeof(void));

would result in a compilation error because sizeof(void) is an invalid expression in C. The type void carries no size information, rendering this operation undefined and therefore rejected by the compiler.

Sizeof(void) in GCC: An Exception

Surprisingly, the sizeof(void) expression compiles in the GNU C compiler (GCC). It evaluates to 1, indicating a single byte of memory. However, this behavior is not standard and varies across different compilers and architectures.

Pointer Increment with Void Pointer

Your question about incrementing p with p raises an interesting concept. Since void has no size, the p operation becomes meaningless. The pointer p is not pointing to any specific data type or value, so incrementing it would not have any effect on its value.

In summary, void in C is a data type without size and cannot be used for memory allocation or variable declarations. The sizeof(void) expression is generally invalid, but may behave differently in specific compilers like GCC. Due to its lack of size, attempting to increment a void pointer with p has no meaningful outcome.

The above is the detailed content of Why is `sizeof(void)` invalid in C, but evaluates to 1 in GCC?. For more information, please follow other related articles on the PHP Chinese website!