pointers

问题 My code's aim is to take in 2 command line arguments (inclusive of programme name), and to print out responses as shown based on the given 2nd command line argument. If the command line argument is an integer, the user's input is accepted or "Success"and if it as anything else (e.g. a string or more than one command line argument), it will be Null and the error message will be shown. This is for CS50 caesar for those who are familiar My Code is as follows: #include <stdio.h> #include <cs50.h>

问题 My code's aim is to take in 2 command line arguments (inclusive of programme name), and to print out responses as shown based on the given 2nd command line argument. If the command line argument is an integer, the user's input is accepted or "Success"and if it as anything else (e.g. a string or more than one command line argument), it will be Null and the error message will be shown. This is for CS50 caesar for those who are familiar My Code is as follows: #include <stdio.h> #include <cs50.h>

问题 I'm declaring character array as char* string. And then I declare other pointer which again refer to original string, then when I'm going to change any thing on that string, at runtime program throws segmentation fault. #include <string.h> #include <ctype.h> int main(void) { char* s = "random"; char* t = s; *t = 'R'; // ----> Segmentation fault t[0] = toupper(t[0]); // ----> Segmentation fault *s = 'R'; // ----> Segmentation fault s[0] = 'R'; // ----> Segmentation fault printf("s is : %s ,

问题 I'm declaring character array as char* string. And then I declare other pointer which again refer to original string, then when I'm going to change any thing on that string, at runtime program throws segmentation fault. #include <string.h> #include <ctype.h> int main(void) { char* s = "random"; char* t = s; *t = 'R'; // ----> Segmentation fault t[0] = toupper(t[0]); // ----> Segmentation fault *s = 'R'; // ----> Segmentation fault s[0] = 'R'; // ----> Segmentation fault printf("s is : %s ,

问题 I am aware that we cannot read data into an uninitialized char pointer using fgets. There are quite a few questions relating to this very point here on stackoverflow. All the answers point to the fact that you can't load data into an uninitialized pointer variable. The program shown in the first code snippet is able to populate the first uninitialized char pointer (*str2) using fgets but, crashes while trying to read data into the second uninitialized char pointer (*str3). I can get it to

问题 I am aware that we cannot read data into an uninitialized char pointer using fgets. There are quite a few questions relating to this very point here on stackoverflow. All the answers point to the fact that you can't load data into an uninitialized pointer variable. The program shown in the first code snippet is able to populate the first uninitialized char pointer (*str2) using fgets but, crashes while trying to read data into the second uninitialized char pointer (*str3). I can get it to

问题 I'm trying to get std input to scan in two 2d parallel arrays (arrAtk, arrDef) of x rows (x<100), and y columns (y<1,000,000). But y is a variable length in each row. The first line of input is x for the number of rows in each array. the second line is y for the number of columns in the first row. Following that is y integers to be read into the arrAtk array. Then another y integers to be read into the arrDef array. Directly following is an int y for the number of columns in the next two rows

问题 int main() { int a = 2; // address is 0x7ffeefbff58c int *b = &a; std::cout << "address of a: " << b << std::endl; return 0; } I have my int variable a at address 0x7ffeefbff58c, but can I directly assign int* b with 0x7ffeefbff58c? I tried int * b = 0x7ffeefbff58c; But there is an error says "cannot initialize a variable of type 'int *' with an rvalue of type 'long'", so do I have to use the address of a (&a) to initialize the pointer? or there is other way to do it? 回答1: can I directly

问题 I want to define a pointer to a subarray. For a simple range this is easily done by pointer => array(i:j) , but I can't figure out how to do this for a map like k=[k1,k2,k3] . If I would define another array I could use a loop like array2=[(array1(k(j)),j=1,size(k,1))] . But it isn't possible to assign a pointer in a similar way ( pointer => [(array1(k(j)),j=1,size(k,1))] ) since the r.h.s. of the expression seems to define another variabel which then not even has the target attribute. For

问题 Is it possible to create a pointer to a function pointer, i.e. int32_t (*fp[2])(void) = {test_function1, test_function_2}; // initialize a function pointer <unknown> = fp; What needs to be written in place of unknown? With "normal" arrays, I could do this: int a[2] = {0, 1}; int* p = a; Many thanks in advance. 回答1: typedef void(*func_ptr_t)(void); // a function pointer func_ptr_t* ptr_to_func_ptr; // a pointer to a function pointer - easy to read func_ptr_t arr[2]; // an array of function