pointers

问题 I am trying to use reflection to set a pointer. elasticbeanstalk.CreateEnvironmentInput has a field SolutionStackName which is of type *string . I am getting the following error when I try to set any value: panic: reflect: call of reflect.Value.SetPointer on ptr Value Here is my code: ... newEnvCnf := new(elasticbeanstalk.CreateEnvironmentInput) checkConfig2(newEnvCnf, "SolutionStackName", "teststring") ... func checkConfig2(cnf interface{}, key string, value string) bool { log.Infof("key %v,

问题 I need a way to pass an array to char* from Python using ctypes library to a C library. Some ways I've tried lead me to segmentation faults, others to rubbish info. 回答1: As I've been struggling with this issue for some time, I've decided to write a small HowTo so other people can benefit. Having this C piece of code: void passPointerArray(int size, char **stringArray) { for (int counter=0; counter < size; counter++) { printf("String number %d is : %s\n", counter, stringArray[counter]); } } We

问题 I'm implementing linked lists using structures. I have a structure - typedef struct llist node; typedef node *nodeptr; struct llist { int data; nodeptr next; }; Now lets say I declare a variable nodeptr *ptr; . How do I access the members data and next using ptr ? 回答1: You deference the first pointer and then the second one. To access the data and next in the structure statement would like this (*ptr)->data = 5; (*ptr)->next = temp; brackets around ptr is required since -> has higher priority

问题 I'm implementing linked lists using structures. I have a structure - typedef struct llist node; typedef node *nodeptr; struct llist { int data; nodeptr next; }; Now lets say I declare a variable nodeptr *ptr; . How do I access the members data and next using ptr ? 回答1: You deference the first pointer and then the second one. To access the data and next in the structure statement would like this (*ptr)->data = 5; (*ptr)->next = temp; brackets around ptr is required since -> has higher priority

问题 Consider the following code: int a[25][80]; a[0][1234] = 56; int* p = &a[0][0]; p[1234] = 56; Does the second line invoke undefined behavior? How about the fourth line? 回答1: It's up to interpretation. While the contiguity requirements of arrays don't leave much to the imagination in terms of how to layout a multidimensional arrays (this has been pointed out before), notice that when you're doing p[1234] you're indexing the 1234th element of the zeroth row of only 80 columns. Some interpret

问题 I'm not able to understand this statement of code that I came across during my interview. int(*(*ptr[3])(char*))[2]; I've tried looking at an IDE but all I have is that it is an array of data type int (*(*[3])(char *)) I wasn't able to understand this. 回答1: May be you could just break it down one at a time to understand the syntax better. First start up with a simple definition without the array notation int(*(*ptr)(char*)); So ptr is a function pointer that takes a char pointer as an

问题 I am writing a C code to find the middle of linked list. I understood the logic but was unable to figure out how pointers are being used. What is the difference in the way Node *head and Node** head_ref work? void middle(struct Node *head) ; void push(struct Node** head_ref, int new_data) ; 回答1: In the first function header, *head is a pointer to a node object which is allocated somewhere in memory: void middle(struct Node *head); _____________________ | | *head --> | Node object | | [val=1][

问题 What is a pointer? What is dereferencing? If p is a pointer, what is the difference between *p = some_value and p = other_value ? What does p = &some_variable mean? What is a NULL pointer? What happens when you dereference a NULL pointer? 回答1: Get a stack of yellow sticky notes, a pencil, an eraser, and a pen. Take a sticky note. Divide it with a horizontal line. Write "note #1" on it with a pen in the top part. (This mark is permanent). Write "7" with a pencil in the bottom part. Stick it to

问题 C#'s ref locals are implemented using a CLR feature called managed pointers, that come with their own set of restrictions, but luckily being immutable is not one of them. I.e. in ILAsm if you have a local variable of managed pointer type, it's entirely possible to change this pointer, making it "reference" another location. (C++/CLI also exposes this feature as interior pointers.) Reading the C# documentation on ref locals it appears to me that C#'s ref locals are, even though based on the

问题 A pointer * and a reference & in Rust share the same representation (they both represent the memory address of a piece of data). What's the practical differences when writing code though? When porting C++ code to Rust can they be replaced safely (c++ pointer --> rust pointer, c++ reference --> rust reference ) ? 回答1: Use references when you can, use pointers when you must. If you're not doing FFI or memory management beyond what the compiler can validate, you don't need to use pointers. Both