dereference

问题 This question already has an answer here: Why doesn't my program seg fault when I dereference a NULL pointer inside of malloc? 4 answers I\'ve come across a snippet of code that to me should crash with a segmentation fault , and yet it works without a hitch. The code in question plus relevant data structure is as follows (with associated comment found right above): typedef struct { double length; unsigned char nPlaced; unsigned char path[0]; } RouteDefinition* Alloc_RouteDefinition() { // NB:

问题 I am learning C language and quite confused the differences between ++*ptr and *ptr++ . For example: int x = 19; int *ptr = &x; I know ++*ptr and *ptr++ produce different results but I am not sure why is that? 回答1: These statements produce different results because of the way in which the operators bind. In particular, the prefix ++ operator has the same precedence as * , and they associate right-to-left. Thus ++*ptr is parsed as ++(*ptr) meaning "increment the value pointed at by ptr ,". On

问题 This is a program I ran: #include <stdio.h> int main(void) { int y = 1234; char *p = &y; int *j = &y; printf(\"%d %d\\n\", *p, *j); } I am slightly confused about the output. What I\'m seeing is: -46 1234 I wrote this program as an experiment and wasn\'t sure what it was going to output. I was expecting possibly one byte from y . What is happening \"behind-the-scenes\" here? How does dereferencing p give me -46 ? As pointed out by others, I had to do explicit casting to not cause UB. I am not

问题 Can you dereference a variable id retrieved from the id function in Python? For example: dereference(id(a)) == a I want to know from an academic standpoint; I understand that there are more practical methods. 回答1: Here's a utility function based on a comment made by "Tiran" in the discussion Hophat Abc referenced that will work in both Python 2 and 3: import _ctypes def di(obj_id): """ Inverse of id() function. """ return _ctypes.PyObj_FromPtr(obj_id) if __name__ == '__main__': a = 42 b =

问题 The dot ( . ) operator is used to access a member of a struct, while the arrow operator ( -> ) in C is used to access a member of a struct which is referenced by the pointer in question. The pointer itself does not have any members which could be accessed with the dot operator (it\'s actually only a number describing a location in virtual memory so it doesn\'t have any members). So, there would be no ambiguity if we just defined the dot operator to automatically dereference the pointer if it

问题 I\'m learning/experimenting with Rust, and in all the elegance that I find in this language, there is one peculiarity that baffles me and seems totally out of place. Rust automatically dereferences pointers when making method calls. I made some tests to determine the exact behaviour: struct X { val: i32 } impl std::ops::Deref for X { type Target = i32; fn deref(&self) -> &i32 { &self.val } } trait M { fn m(self); } impl M for i32 { fn m(self) { println!(\"i32::m()\"); } } impl M for X { fn m

问题 Please include an example with the explanation. 回答1: Reviewing the basic terminology It's usually good enough - unless you're programming assembly - to envisage a pointer containing a numeric memory address, with 1 referring to the second byte in the process's memory, 2 the third, 3 the fourth and so on.... What happened to 0 and the first byte? Well, we'll get to that later - see null pointers below. For a more accurate definition of what pointers store, and how memory and addresses relate,