pointers

问题 I tested the keyword fixed with array and string variables and worked really well but I can't use with a single variable. static void Main() { int value = 12345; unsafe { fixed (int* pValue = &value) { // problem here *pValue = 54321; } } } The line fixed (int* pValue = &value) causes a complier error. I don't get it because the variable value is out of the unsafe block and it is not pinned yet. Why can't I use fixed for the variable value ? 回答1: This is because value is a local variable,

问题 The following code gives a segmentation fault. I am not able to figure out as to why. Please see.. #include <stdio.h> #include <stdlib.h> int main() { int **ptr; int *val; int x = 7; val = &x; *ptr = (int *)malloc(10 * sizeof (*val)); *ptr[0] = *val; printf("%d\n", *ptr[0] ); return 0; } on debugging with gdb, it says: Program received signal SIGSEGV, Segmentation fault. 0x0804843f in main () at temp.c:10 *ptr = (int *)malloc(10 * sizeof (*val)); Any help regarding the matter is appreciated.

问题 I'm wondering if a pointer may point to a cpu register since in the case it may not, using reference instead of pointer where possible would give compiler opportunity to do some optimizations because the referenced object may reside in some register but an object pointed to by a pointer may not. 回答1: In general, CPU registers do not have memory addresses, though a CPU architecure could make them addressable (I;m not familar with any - if someone knows of one, I'd appreciate a comment).

问题 int (*ptr)[10]; I was expecting ptr to be an array of pointers of 10 integers. I'm not understanding how it is a pointer to an array of 10 integers. 回答1: ptr is of type "pointer to array of 10 int". In your declaration it is uninitialized so it doesn't point to any object. To make it point to an array: int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // initialize in the declaration: int (*ptr) [10] = &arr; // or after: int (*ptr) [10]; ptr = &arr; 回答2: I like to read it like this: (great

问题 int (*ptr)[10]; I was expecting ptr to be an array of pointers of 10 integers. I'm not understanding how it is a pointer to an array of 10 integers. 回答1: ptr is of type "pointer to array of 10 int". In your declaration it is uninitialized so it doesn't point to any object. To make it point to an array: int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // initialize in the declaration: int (*ptr) [10] = &arr; // or after: int (*ptr) [10]; ptr = &arr; 回答2: I like to read it like this: (great

问题 In this code, I see that they declare a pointer before initializing SDL: int main(int argc, char* argv[]) { SDL_Window *window; // Declare a pointer SDL_Init(SDL_INIT_VIDEO); // Initialize SDL2 // Create an application window with the following settings: window = SDL_CreateWindow( "An SDL2 window", // window title SDL_WINDOWPOS_UNDEFINED, // initial x position SDL_WINDOWPOS_UNDEFINED, // initial y position 640, // width, in pixels 480, // height, in pixels SDL_WINDOW_OPENGL // flags - see

问题 I need to create a program which calculates the cumulative sum of a dynamically allocated vector and the vector should be filled with random values (not values from stdin) ​​using only pointers . I couldn't think of a version that uses only pointers (i'm kinda new to this matter). This is the code I have so far: #include <stdio.h> #include <malloc.h> int main() { int i, n, sum = 0; int *a; printf("Define size of your array A \n"); scanf("%d", &n); a = (int *)malloc(n * sizeof(int)); printf(

问题 I was writing a program in C++ where I need to have a 2d grid of pointers which point to objects which are stored in a vector. I tested out some part of the program and saw strange results in the output. I changed the objects to integers and removed everything non-essential to cut it down to the code snippet below, but I still get a weird output. vector<vector<int*>> lattice(10, vector<int*>(10));//grid of pointers vector<int> relevant;//vector carrying actual values onto which pointers will

问题 Can some explain me the behavior of this C program I was trying to understand its behavior... #include<stdio.h> float x = 3.33,*y,z; int *a,b; int main() { a = (int *)&x; b = (int)x; y = (float *)a; z = (float)b; printf("\nOriginal Value of X: %f \ncasting via pointer A:%d and back Y: %f \ndirect casting B:%d and back Z:%f\n",x,*a,*y,b,z); } Output: Original Value of X: 3.330000 casting via pointer A:1079320248 and back Y: 3.330000 direct casting B:3 and back Z:3.000000 OK so why is the value

问题 Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 3 years ago . Improve this question I have defined structs in header file typedef struct tDLElem { int data; struct tDLElem *lptr; struct tDLElem *rptr; } *tDLElemPtr; typedef struct { tDLElemPtr First; tDLElemPtr Act; tDLElemPtr Last; } tDLList; And I have this code void DLInsertFirst (tDLList