dereference

问题 I was learning about C++ pointers and the -> operator seemed strange to me. Instead of ptr->hello(); one could write (*ptr).hello(); because it also seems to work, so I thought the former is just a more convenient way. Is that the case or is there any difference? 回答1: The -> operator is just syntactic sugar because (*ptr).hello() is a PITA to type. In terms of the instructions generated at the ASM level, there's no difference. In fact, in some languages (D comes to mind), the compiler figures

问题 From the Rust guide: To dereference (get the value being referred to rather than the reference itself) y , we use the asterisk ( * ) So I did it: fn main() { let x = 1; let ptr_y = &x; println!("x: {}, ptr_y: {}", x, *ptr_y); } This gives me the same results (x=1; y=1) even without an explicit dereference: fn main() { let x = 1; let ptr_y = &x; println!("x: {}, ptr_y: {}", x, ptr_y); } Why? Shouldn't ptr_y print the memory address and *ptr_y print 1? Is there some kind of auto-dereference or

问题 From the Rust guide: To dereference (get the value being referred to rather than the reference itself) y , we use the asterisk ( * ) So I did it: fn main() { let x = 1; let ptr_y = &x; println!("x: {}, ptr_y: {}", x, *ptr_y); } This gives me the same results (x=1; y=1) even without an explicit dereference: fn main() { let x = 1; let ptr_y = &x; println!("x: {}, ptr_y: {}", x, ptr_y); } Why? Shouldn't ptr_y print the memory address and *ptr_y print 1? Is there some kind of auto-dereference or

问题 I am just starting C++. I am a bit confused about the return type of assignment and dereference operator. I am following the book C++ Primer. At various occasions, the author says that the return type of assignment operator is reference to the type of left hand operand but later on, he says that the return type is the type of the left hand operand. I have referred C++11 Standard Sec. 5.17, where the return type is described as "lvalue referring to left hand operand". Similarly, I can't figure

问题 I have a problem when my application crashes with this error message from VS: "Debug assertion failed! (...) Expression: vector iterator not dereferencable". The thing is, it happens during using vector's push_back. Here is the code. It is my BigInt library, that I decided to implement as an exercise. The bug is hidden in my TestBigInt class, that I created to (surprisingly) test BigInt. The code is admittedly quite long, but I narrowed the bug to a single piece of that. This is the input I

问题 According to Oracle I should be able to apply methods like .intValue() and .compareTo() to doubles but when I write dbl.toString() in NetBeans, for example, the IDE tells me that doubles can't be dereferenced. I can't even cast them to Integers in the form (Integer) dbl ! I have JDK 1.6 and NetBeans 6.9.1. What's the problem here? 回答1: The problem is your understanding of objects vs. primitives. More than anything else, you just need to recognize that the capitalized names are object classes

问题 As I'm quite new to C, there's something I don't yet get about pointers. I'd like to check wether a command line argument is integer or not, but in a separate function, so that I pass in the pointer of the argv array. int main(int argc, char* argv[]){ if(check(argv)){ // Do stuff to argv[1] } } int check(char* p){ // Test wether p+1 is int return 1; } I have tried several things mostly resulting in weird printf's (when printing the dereferenced pointer to test the value). int i = atoi(argv[1]

问题 I seem to have a problem with a simple program that is supposed to count various character types in a file. It always prints zeroes even though the file is not empty at all. I think it has something to do with pointers, could be wrong. I would also like to know if initializing variables is necessary in this case? // fun.h void count_char(FILE *f, unsigned *newl, unsigned *let, unsigned *num, unsigned *spec_char); // main.c #include <stdio.h> #include "fun.h" int main() { unsigned newline = 0,

问题 I just installed PHP 5.4 and now that it supports array dereferencing I want to use that in my projects. Problem is that I'm working with Dreamweaver (CS6) and it gives me a syntax error for using the array brackets after the function parantheses. Is there any way to mess around with Dreamweaver's syntax support (or maybe just tuning the syntax highlighting in the configuration/CodeColoring directory may be enough)? 回答1: I would suggest to download another Editor if you work with PHP. Some

问题 I'm new to Oracle Objects and I have a problem. I don't know how to dereference an item from a VARRAY of REFs. Below is some source code that reproduces the problem that I have. The error is: PLS-00306: Wrong number or types of arguments in call to 'DEREF' DROP TYPE LOC FORCE / DROP TYPE LIST_LOC FORCE / DROP TYPE PIZ FORCE / CREATE OR REPLACE TYPE LOC AS OBJECT( NAME VARCHAR2(30), MEMBER FUNCTION GET_NAME RETURN VARCHAR2 ) / CREATE OR REPLACE TYPE BODY LOC AS MEMBER FUNCTION GET_NAME RETURN