Function opcode in C

Question

I was reading an article x86 API hooking demystified about x86 hooking, and I came across this code:

if(*function_A == 0xe9) {
    printf("Hook detected in function A.\n");
}

It seems that this code tests whether the opcode of the function is a jump. My question is about the syntax *function_A. what is this syntax? Does it return the opcode of a function in C? I made a lot of research but I didn't find any documentation on this feature

EDIT

I thought I added the link to the article but I just noticed I forgot to add it. Link added in case it helps.

Answer 1

No, you cannot dereference a function pointer to get at the underlying code.

This is probably done by introducing a different pointer, and relying on the particular platform "doing the right thing", where "right" means "what I want to do".

Something like:

const unsigned char *function_A = (unsigned char *) printf; /* Any function. */

This is not portable, and will generate compiler warnings since function and data pointers are not compatible. On e.g. x86, it will probably "work".