C/C++ :: Why Do Void Function Pointers EXECUTE Arrays Of Hexcode
Dec 23, 2012
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?
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May 14, 2014
As part of my ongoing c programming education, I have written a program to use void pointers in a function,
Code:
#include <stdio.h>
#define MAX_NUMBERS 10
size_t size(void *object);
int main(void) {
}
[code]....
Now I think that the result 4 is the size of the pointer, so I'm confussed as why it doesn't give me the same result as 40.
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Aug 31, 2014
I'm having issues with pointers and relationship operators in C.
I need to find a max and min value in a void function using pointers. max and min would work if they had values. mul works, because you can just do math operations with pointers.
There are 0 errors and warnings; but max and min are never going to work as is.
Clearly I'm missing something.
#include <stdio.h>
#include <stdlib.h>
void max(int *a, int *b, int *c, int *d, int *result);
void min(int *a, int *b, int *c, int *d, int *result);
void mul(int *a, int *b, int *c, int *d, int *result);
int main()
[Code]...
Your job will be to create a program that uses pointers. Your output must be done in the main function and the calculations MUST be done in the three functions. Therefore you MUST use pointers correctly.
You must declare and implement the following 3 functions. Below are the three prototypes that you must use in this program.
void max(int *a, int *b, int *c, int *d, int *result);
void min(int *a, int *b, int *c, int *d, int *result);
void mul(int *a, int *b, int *c, int *d, int *result);
The functions have the following meaning:
max
finds the max value of a,b,c,d and stores the largest value in result.
min
finds the min value of a,b,c,d and stores the largest value in result.
mul
multiplies a * b * c and divides by d. Stores that value in result.
Below is an example input/output. This input will be read in via the keyboard (use scanf).
input
output (note that user input is shown in bold)
1 2 3 4
Enter the 4 numbers: 1 2 3 4
The max is 4. The min is 1. (a * b * c) / d = 1
100 3 201 103
Enter the 4 numbers: 100 3 201 103
The max is 201. The min is 3. (a * b * c) / d = 585
Your output MUST match exactly the output below for the input from above. Your program must compile, failure to do so will result in 0 points. */
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Feb 12, 2014
I'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.
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Nov 10, 2014
I have a .txt file that I need to input into two parallel arrays. The first array needs to be on dimension and the second needs to be two dimensions.
This is a sample from the .txt file:
Australia62.762.163.359.7
Austria052.853.154.6
Belgium30.430.327.525.3
Canada61.356.257.754.5
Chile026.425.431.1
CzechRepublic038.327.325.2
Denmark65.067.162.355.0
Estonia51.732.929.834.3
Finland55.242.942.143.3
France35.728.330.228.8
Germany56.447.242.646.6
Greece30.326.925.013.1
Hungary032.521.818.6
Iceland068.271.666.0
this is what I have for code so far:
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
using namespace std;
const int SIZE = 40;
const int COLUMN = 5;
void getData(ifstream& inf, string n[], double tstData[][COLUMN], int count);
[Code] .....
when I compile and run the code and have it display it does not read the first item into the 1-d array, instead it appears to read the 4th number from the left into the 1-d array and then into the second spot in the 2-d array, then again in its proper place and finally it has this number repeating through the rest of the arrays:
-92559631349317830000000000000000000000000000000000000000000.00 followed by the number 59.7 from the .txt and the long number again.
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Feb 25, 2015
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.
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Apr 15, 2013
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] ;
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Nov 25, 2013
how can i use the void pointers? i understand that can recive an adress variable(&). but can recive a value?
Code:
int a=5;
void *d;
b=&a;
b=100;//???
why i can't do these?
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Feb 13, 2014
I am trying to add data to a queue with the following simplified code:
Code:
typedef struct Queue {
void * data;
int head;
int tail;
int elementSize;
My question is, how do I move the queue->data pointer to the correct memory location in order to copy given data to head? The code above inside memcpy gives med the error: "expression must be a pointer to a complete object type".
Do I need an extra pointer to be able to navigate between the queue's head and tail, and keep queue->data as a reference to the first byte of the allocated memory, or is it possible with only queue->data?
Edit. Just noticed I have mixed up head and tail. The enqueued data should probably go to the Queue's tail and not the head. However, the problem is still the same.
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Jan 11, 2014
I want to know how to dereference a void pointer through the way of typing it.
Lets just say that I malloc'd a huge bunch of memory and i can do whatever i want
void* randomData = malloc ( 1000000 );
And i decide to make my own virtual 'int'
I am not sure how to do this.
*( int* ) ( randomData + 10 ) = ( int ) 323453 //323453 can be an int variable aswell
Im not sure if this is the right way to do perform a dereference.
This is an overview of what has to be done:
-The pointer has to be dereferenced
-Cast the pointer as an int pointer so we can change it like a normal 4-byte int
-Perform pointer arithmetic, so that the int can be placed anywhere we want
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Jul 13, 2014
I am trying to find the distance between two void pointers, so I can follow this distance to a certain pointer in a vector when given only the previous element in that vector.
int distance = (char*) prev - (char*) first;
next = (char*) cv->elems + cv->elemsz + distance;
Basically, prev and first are void pointers. I am trying to cast them into a char, subtract the first element in the vector from the previous one, and then use this distance to determine what the next element in the vector is. However, it is not working. I am not sure how to do this. To complicate matters, prev is a const void *.
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Jan 21, 2014
This code work perfectly, as follows.
Code #A:
#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
typedef std::vector <void *> gr_vector_void_star;
gr_vector_void_star output_items;
[Code] .....
Output of above code #A:
char * sentence = "Angel";
for (int i=0; i < 5; i++)
{ out[i] = sentence[i]; } // error: invalid conversion from 'char' to 'char*' [-fpermissive]
It fails to compile with error message "invalid conversion from 'char' to 'char*'".
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Nov 8, 2013
I want to write a code that gets three values from the user and puts them into three arrays. When the user enters -999, I want to print out a chart showing all the values they put in. This is what I have so far but it wont build. It tells me std::string is requested, but I'm not sure where to put it, and printArrays is declared void. How can I fix this?
#include <iostream>
#include <string>
using namespace std;
const int ARSIZE = 400;
void printArrays (string reportTitle, int levelsArray[], int scoresArray[], int starsArray[], int i);
[Code] ....
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Mar 14, 2013
Is it possible to write a program such that it will automatically execute the function in queue base on their priority even if user programmed it randomly?
Code:
function1(){ very_important; }
function2(){ important; }
function3(){ less_important; }
int main() { // Programmed by user
function3;
function1;
function2;
//Output: Program will execute function1, 2 and lastly 3.
}
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Feb 17, 2013
For easier debugging, I would like to execute an own (predefined) function while beeing in a breakpoint (e.g. print some variables to a file).
Does there exists such a feature?
e.g.
- run program to a breakpoint
- a) press a keyboard-function-key (which calls that predefined function)
- b) or hover with cursor over a variable (and modify somehow the routine which shows its content on the screen)?
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Mar 5, 2014
I have simple LCd_call function . I am calling this function from main . I wanted to call this function once. problem i am facing here, When lcd_call function being called. It enter the cases but instead of staying paricular case it coming back and starting case 1 iteslf . for every 6s it change the case to 1:
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Feb 17, 2013
I would like to implements something in my code that clears the value of my variables when the user closes the console. How to do that or the program clears the values automatically?
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Feb 11, 2013
I wish to add the item 'Website' to an MFC Dialog app System Menu so that it can activate the following method:
Code:
void CMyDlg::OnWebpage()
{
ShellExecute( NULL, NULL, _T("[URL]..."), NULL, NULL, 0 );
}// OnWebpage()
I have tried this:
Code:
#define IDM_WEBSITE (WM_USER + 101)
//..
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
pSysMenu->AppendMenuW(MF_STRING, IDM_WEBSITE, _T("Website"));
}
[Code]...
The code compiles without error but and the 'website' item appears on the System Menu but it doesnt do anything.
I've inspected the following but don't really understand how it works and it seems to me there should be a simpler way to accomplish my end.
Modifying the System Menu By John Simmons 26 Jan 2007 [URL]....
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Dec 24, 2013
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?
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Apr 14, 2013
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].....
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Feb 11, 2013
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] .....
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Jun 27, 2013
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] .....
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Jul 17, 2013
Merging two arrays together using pointers!
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Aug 30, 2013
I 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]....
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Feb 6, 2013
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.
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Aug 3, 2014
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.
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