double-pointer

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 I have a question about reading a file character by character and counting it in C here's my code down below void read_in(char** quotes){ FILE *frp = fopen(IN_FILE, "r"); char c; size_t tmp_len =0, i=0; //char* tmp[100]; //char* quotes[MAX_QUOTES]; //char str = fgets(str, sizeof(quotes),frp); while((c=fgetc(frp)) != EOF){ if(frp == NULL){ printf("File is empty!"); fclose(frp); exit(1); } else{ if(c != '\n'){ printf("%c",c); c=fgetc(frp); tmp_len++; } } char* tmp = (char*)calloc(tmp_len+1,

问题 I am getting a little confused as to how to properly allocate memory for double pointers. My code causes a segment fault the second time it attempts to store a value at the 2nd index of the first UCHAR pointer array. Any assistance would be appreciated. assigning my double pointer: width = BMP_GetWidth (bmp); height = BMP_GetHeight (bmp); depth = BMP_GetDepth (bmp); r = (UCHAR **) malloc(sizeof(UCHAR *) * height); g = (UCHAR **) malloc(sizeof(UCHAR *) * height); b = (UCHAR **) malloc(sizeof

来源： https://stackoverflow.com/questions/63514647/how-to-set-value-of-struct-indirectly-in-c

问题 So this static_cast code is totally legal: int n = 13; void* pn = static_cast<void*>(&n); void** ppn = &pn; Yet this has to be made into a reinterpret_cast to compile: int n = 13; int* foo = &n; void** bar = static_cast<void**>(&foo); If I don't change it I get the error: error C2440: static_cast : cannot convert from int ** to void ** note: Types pointed to are unrelated; conversion requires reinterpret_cast , C-style cast or function-style cast So I take it the issue is "the types are

问题 How can i access to a duble pointer in a struct pointer?? with the code bellow, calling addBow() give me a Segmentation fault (core dumped) error typedef struct { int size; tCity **cities; }tGraph; //para iniciar el grafo void initGraph(tGraph *graph, int size) { graph = (tGraph*)malloc(sizeof(tGraph)); graph->cities = (tCity**)malloc(sizeof(tCity*) * size); graph->size = size; } //agrega un arco entre ciudades void addBow(tGraph *graph, int id, tCity *city) { if ( graph->cities[id] == NULL )

问题 I'm a COBOL programmer , and my latest project is to connect a COBOL application to a SQLite3 database. I have been following this guide, and their solution is exactly what I would need in my COBOL application. I have successfully managed to create, connect, insert data and close the database, but the problem arises when I try to select data from the database. In the tutorial, they use a callback with double pointers. static int callback(void *NotUsed, int argc, char **argv, char **azColName)

问题 I have to write a function which takes in 2 double pointers (both to char type). The first double pointer has a string of query values and the 2nd one has stopwords. The idea is to eliminate the stopwords from the query string and return all the words without those stopwords. For example Input - query: “the”, “new”, “store”, “in”, “SF” stopwords: “the”, “in” OUTPUT new store SF I have written the following code while trying to use strtok which takes in only single pointers to char types. How

问题 Please find the code snippet as shown below: #include <stdio.h> int My_func(int **); int main() { int a =5; int *p = &a; My_Func(&p); printf("The val of *p is %d\n,*p); } void My_Func(int **p) { int val = 100; int *Ptr = &val; *p = Ptr; } How does by using a double pointer as a argument in my_Func function and making change of value reflects the same in the main function but if we use a single pointer in My_Func does not change the value in main?Please do explain me with examples if possible