I am trying to use pointers to arrays in my function.
I can get the pointers to work outside of a function but I just can't figure out how to make them work in my function.jwhittle58, on 25 February 2015 - 06:06 PM, said:
I am trying to use pointers to arrays in my function. I can get the pointers to work outside of a function but I just can't figure out how to make them work in my function.
I know how to use functions pointers in C and C++ and I know if you have something like
char buf[] = {
0x48, 0xb8, 0x3c, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x48, 0xbf, 0x02, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x0f, 0x05
};
((void (*) (void))buf)();
That this will execute those binary instructions in hexadecimal notation BUT WHY? I don't get why that works since that's an array of data not a function?
I'm trying to write a function that takes a 32bit address and a data to store at this address.
I'm wanting to take the 32 bit memory address eg 0x12345678 and split it
into 4 x 2 bytes
12, 34, 56, 78
then each of the 4 entries is at most a 256 entry array.eg
FF, FF, FF, FF
So in this example, 0x12 points to 0x34 in the second array, which points to 0x56 in the third array, which finally points to 0x78 in the last array. This last array holds the actual data.
After successfully doing 0x12345678, say I might get a read for 0x1234AABB. So, the first and second pointers already exist, but I then have to create and write to dynamically created arrays.
The arrays need to have all entries set to NULL so that i know whether to follow the pointers to overwrite a previously entered value or create new arrays and pointers.
It all looks good and simple in the pseudo code I've written up but I'm having trouble coding it. I'm currently trying to deal with the first entry case, ie all array elements are NULL, but I'm getting confused with the pointers and creation of new arrays.
void cpu::store(unsigned int mem_add,unsigned int mem_val) {
int first = (mem_address&4278190080)>>24;
int second = (mem_address&16711680)>>16;
int third = (mem_address&65280)>>8;
int fourth= (mem_address&255);
[Code] .....
A1 has been declared as
int* A1[256] ;
So when if you want to change the values themselves for example in an array (just for example) this is valid;
void test(int* test)
{
test[0] += 10;
}
int bob[] {1, 3, 5};
If you did that bob[0] would not equal 11. All well and good right?
Now if you do this?
int sally = 33;
test(sallay);
This wouldn't work at all you actually have to use
void test(int& test)
{
test += 10;
}
how the memory addresses etc. are working here? I don't understand why you need to use & the reference operator if it's not an array? Why wouldn't that still work?
Here is my program to look up words. How do I use character pointers instead of using arrays?
Code:
#include <stdio.h>
struct entry
{
[Code].....
I am having troubles with dynamic arrays and pointers. All the errors are of that kind. I think when I am assigning malloc to an array we assign to its address.
Code:
/*Create an array of genes of the large matrix*/
gene_t gene,gene1,gene2;
gene=malloc(INITIAL*sizeof(gene2)); Code:
while(...) {
if (gene_num==current_size){
[Code] .....
Set an Array (a[10]) and a Pointer to that array (*pa) and code a loop (for( ; ; loop) that will advance that pointer (*pa) and will set a new content into it with each loop. that means that in the end of the day, my program will automatically set content to each cell of the array by promoting the pointer by 1 and add the sum to that pointer.
When I run the program it prints the address of the cells instead the value of it.
Code:
#include <stdio.h>
void main() {
float a[11], *pa; // Array and ptr set.
int i; // counter for the loop.
pa = a;
for (i=0 ; i<=10 ; i++) // the loop itself.
[Code] .....
Merging two arrays together using pointers!
View 4 Replies View RelatedI came across the below code snippet in a project and was not sure how value of variable "response" is computed. Here as we can see, pic_data holds two one dimensional arrays but "response" access both the single dimensional array as two dimensional array.
Code:
#define MAX 100
#define MAXBUF 100
u32 response;
u32 index;
}
[code]....
I have a problem with a pointer and a bidimensional array. Here's the code:
typedef char t_board[5][4];
int i,j;
t_board *copy (t_board b) {
t_board *ptr;
ptr = (t_board *) malloc (sizeof(t_board));
[Code] ...
After this, I print new_board, and its ok; but the following code after the call to copy, crashes. Don't know why. if I remove the statement new_board = copy(some_board); , the code that follows runs ok.
I'm writing quite a large program that needs to work with very large arrays (up to 100 million integers). It is necessary that i can access every point of the array directly (without running through the array) and that I use as little memory as possible. I first wrote the program with pointers that point to allocated heap memory. It works fine but now I wanted to use smart pointers instead (so I'm sure to have no memory leaks). Here's a simple visualization of my problem:
#include <iostream>
#include <memory>
using namespace std;
unique_ptr<int[]> upArray;
int main() {
int nArrayLength = 10;
[Code] ....
There are 2 things that do not work how I would like the to:
1. It wants me to assign the heap memory in one step: unique_ptr<int[]> upArray(new int[nArrayLength]); But I'd like to have the unique_ptr in my Class_Declaration before I know the array length and allocate the memory later.
2. *(upArray + i) = i;
cout << *(upArray + i);
Those lines don't work! How else can I do it.
I am looking for an example of when passing arrays to other data that has pointers,
I understand the terms I would just like to see a small example of code that actually demonstrates this process.
the book I learn from gave a task to write a program which gets a matrix , and we have to write a function that switches 2 columns or rows the user inputs .as far as I know a function can not change variables in the main function without using pointers .so , theoretically, can a function described here can be written without using pointers ? as far as I tried - it can not.
View 9 Replies View RelatedClass with Pointers and Dynamic Arrays
View 2 Replies View RelatedWrite a program that uses a record structure to store a Student Name, Student ID, Test Scores, Average Test Score, and Grade. The program should keep a list of test scores for a group of 6 students. The program should ask for the name, ID, and four test scores for each student. Then the average test score should be calculated and stored. The course grade should be based on the following scale:
Average Test Score Course Grade
------------------ ------------
90 - 100 A
80 - 89 B
70 - 79 C
60 - 69 D
59 or below F
A table should be displayed on the screen listing each student's name, ID, average test score, and course grade. Implement with functions.
My code runs but it isnt returning anything (readable/correct) and i have no clue why. This is what i have so far:
#include <iostream>
using namespace std;
const int columns = 4;
struct StuRec //user defined datatype {
int id[6];
char names[6][20];
[Code] .....
it compiles completely but at the end instead of showing the student name ID average score and class grade it shows.... [URL] .....
Write a program that uses a record structure to store a Student Name, Student ID, Test Scores, Average Test Score, and Grade. The program should keep a list of test scores for a group of 6 students. The program should ask for the name, ID, and four test scores for each student. Then the average test score should be calculated and stored. The course grade should be based on the following scale:
Average Test Score Course Grade
------------------ ------------
90 - 100 A
80 - 89 B
70 - 79 C
60 - 69 D
59 or below F
A table should be displayed on the screen listing each student's name, ID, average test score, and course grade. Implement with functions.
My code runs but it isnt returning anything(readable/correct) and i have no clue why. This is what i have so far:
#include <iostream>
using namespace std;
const int columns = 4;
struct StuRec //user defined datatype {
int id[6];
char names[6][20];
int scores[6][4];
double avg[6];
char grade[6];
}; //semi-colon required
[Code] ...
Code:
typedef struct {
name_t name;
float beta[beta_num];
} gene_t;
[Code] ....
Is gene an array of address ? How come the compare function doesn't work ?
I need to use dynamic memory allocation and use pointers to iterate through the arrays that I have already in this program. I am lost, nothing I do works and where to use the pointers. I am just looking for a push in the right direction so I can finish this project and how I can implement pointers in my program.
#include <iostream>
#include <string>
#include <cstdlib>
#include <iomanip>
#include <stdio.h>
using namespace std;
[Code]...
I am writing a class that dynamically allocates an array that holds a user-defined number of test scores (test scores go from 0 to 10 both included). Once all the test scores are entered and validated (values only between 0 and 10, both included), the array should be passed to a function that sorts them in ascending order. Another function should be called that calculates theaverage of all the scores.The main program should display the sorted list of scores and the average of the scores with appropriate headings.
View 6 Replies View RelatedI'm trying to pass 2 arrays into a void funtion, and return values to one function.
this is the the program I'm working with, after I'm done I have to split it into 3 files, a header, a main, and a separate cpp file for the functions to live in.
#include <iostream>
using namespace std;
void processArrary(int numberCount[], int Numbers[], int intnumberSize, int numberCountSize);
int main() {
int Scores[26] = {76, 89, 150, 135, 200, 76, 12, 100, 150, 28, 178, 189, 167, 200, 175, 150, 87, 99, 129, 149, 176, 200, 87, 35, 157, 189};
int numberCount[8] = { 0 };
[code]...
The goal of this program is to separate and count the groups of numbers then output the amount of numbers in each group. Near as I can tell, everthing should work, but I'm getting all zeros to be displayed in each group.
What are Function pointers , what are the benefits of using it?
View 4 Replies View RelatedI want to scan numbers in from within a function, but have access to them in main, so I tried using pointers to do so:
Code:
// Path Of Exile socket colours simulation
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
[Code].....
I have this simple program:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static unsigned char cmd[]={
0x01,0x80,0x00,0x00,0x00
[Code] .....
All is right except the size. Why does it give 80x1 as size instead of the digit 5?
i'm trying to determine if a number from a file is a prime number using pointers first I wrote a function that determines if the number is a multiple of 7, 11, or 13. Then i wrote a function to see if the number is odd or even. Are they correct? Later i will print the results on screen but i'm extremely confused with pointers and i'm not sure how to write this prime function...
Code:
void divisible(int *n, int *result) {
if (*n % 7 == 0 || n % 13 == 0 || n % 13 == 0) {
*result = 1;
[Code] .....
I'm wondering about the point of pointers to functions. When is it used?I saw the below example. It doesn't make sense to me. I mean we can easily write code that does the same without having to use pointers.
Code:
#include <stdio.h>
int addInt(int a, int b); // Adds 2 integers
int add5to4(int (*function_pointer)(int, int));
int main(void)
{
int sum;
int (*function_pointer)(int, int);
}
[code]....
I'm given a mathematical function F(x) = etc..., the user inputs an initial x point and a final x point. The program finds the integration.
Below is a snippet of code.
/*Typedefs as given by prof*/
typedef double (*mainFunction) (double);
typedef double (*calcArea) (mainFunction, double, double);
int main () {
answer = calcIntegral(mainFunction *curve1, calcArea *calcAreaRect, a, B)/>; /*it doesn't like this line*/
printf("The integral from %lf to %lf is: %.4lf", &a,&b,&answer);
return 0;
}
curve1 is a function that accepts a double and returns a double, calcAreaRect takes mainFunction main(which is F(x) so i stored the fn in curve1), double and double.