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c ++ pointer puzzle

By : G.wei
Date : September 15 2020, 01:00 AM
it helps some times &c is a pointer to a single byte of memory, by casting it to int* you are changing it to a pointer to (usually) 4 bytes of memory however there is still only a single byte of memory in the c variable. Any change performed through the pn pointer will attempt to write 4 bytes of memory to c, this is undefined behaviour.
What is likely happening is that all of your variables are laid out next to each other on the stack so when you write out of the bounds of c the writes overwrite one or more of the adjacent variables. You can't rely on this being the exact behaviour though as it is undefined.
code :

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Solving the Zebra puzzle (aka. Einstein puzzle) using the clpfd Prolog library

By : Davide Pizzoli
Date : March 29 2020, 07:55 AM
it fixes the issue I have been given an exercise to solve the zebra puzzle using a constraint solver of my choice, and I tried it using the Prolog clpfd library. , running your code in SWI-Prolog, I get
code :
?- solve(X),label(X).
X = [3, 5, 2, 1, 4].
?- solve(X).
X = [3, _G3351, _G3354, 1, _G3360],
_G3351 in 4..5,
all_different([_G3351, _G3386, _G3389, 2, _G3395]),
all_different([3, _G3351, _G3354, 1, _G3360]),
_G3386 in 3..5,
all_different([_G3386, _G3444, 1, _G3450, _G3360]),
_G3389 in 1\/3..5,
_G3395 in 1\/3..5,
_G3478 in 2..6,
_G3444 in 2..5,
_G3450 in 2\/5,
all_different([_G3354, 4, 3, _G3450, _G3614]),
_G3360 in 2\/4..5,
_G3354 in 2\/5,
_G3614 in 1..2\/5,
_G3556 in 2..3\/6,
_G3553 in 0..1,
_G3565 in 0..1,
_G3568 in 0..1\/4,
_G3492 in 0..4,
_G3577 in 0..1,
_G3529 in 0..1.

?- solve(X).
X = [3, 5, 2, 1, 4].
?- maplist(in, Vs, [1\/3..4, 1..2\/4, 1..2\/4, 1..3, 1..3, 1..6]), all_distinct(Vs).

?- maplist(in, Vs, [1\/3..4, 1..2\/4, 1..2\/4, 1..3, 1..3, 1..6]), all_different(Vs).
Vs = [_G419, _G422, _G425, _G428, _G431, _G434],
_G419 in 1\/3..4,
all_different([_G419, _G422, _G425, _G428, _G431, _G434]),
_G422 in 1..2\/4,
_G425 in 1..2\/4,
_G428 in 1..3,
_G431 in 1..3,
_G434 in 1..6.

C Code Pointer Puzzle

By : Jewel Mia
Date : March 29 2020, 07:55 AM
it should still fix some issue I'm looking at some code a classmate posted and it has been simplified for the sake of this example: ,
but it segfaults on a 64bit computer
code :
test.c:7:19: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
#include <stdio.h>

int main()
   char *s = "";
   printf("%p %p\n", s, (char*)(int)s);
   return 0;
printf("B1 Points to %p - B2 Points to %p\n", b1, b2);

creating word search puzzle solver in c, Incompatible pointer type and pointer from integer without cast warnings in c

By : tanpham
Date : March 29 2020, 07:55 AM
wish helps you There are too many errors in your code. Here's a working program to get you going in the right direction. I have removed verticalrow and diagonalrow to simplify things.
code :
#include <stdio.h>
#include <string.h>

#define ROW 3
#define COL 4

void horizontalrow(char a[ROW][COL], char *argv[], int argc)
   int i=0,j=0, k =0;
   for(i  = 0; i  < ROW - 1; i++)
      for(j = 0;j <  COL; j++)
            if(a[i][j] == *argv[k] )
               printf("%c appears horizontally at a[%d][%d]\n", a[i][j], i, j);

int main(int argc, char* argv[])
  char a[ROW][COL] = { {'a','b','c','d'},
                       {'x','y','z','d'} };

  horizontalrow(a, argv+1, argc-1);

  return 0;
void horizontalrow(char *a[ROW][COL], char *argv[], int argc)
void horizontalrow(char a[ROW][COL], char *argv[], int argc)
                    //  ^^^ no pointer, just the array.
if(a[i][j] == *argv[k] )
myprogram a b c
printf("%s appears horizontally at a[%d][%d]", a[i][j],i,j);
printf("%c appears horizontally at a[%d][%d]\n", a[i][j], i, j);
int i=0,j=0,k=0;
horizontalrow(a[ROW][COL],argv[k], argc);
horizontalrow(a, argv+1, argc-1);

Char pointer puzzle

By : selvi
Date : March 29 2020, 07:55 AM
Does that help It's perfectly normal to do something like that with pointers. But it can be a bit tricky. If the function does the memory allocation, you will have to pass a pointer to a pointer as an argument, which is possible, but not very common. The Apache Portable Runtime library makes use of this technique.
It is more common to pass a pointer to a buffer and the size of the buffer as arguments, like so:
code :
int your_read(int fd, char *buf, size_t len) {
    return read(fd, but, len);
// called using e.g.:
char the_buffer[1024];
your_read(0, the_buffer, sizeof(the_buffer))
int create_object(struct example **e) {
    *e = malloc(sizeof(**e));
    if (*e == NULL)
        return -1;
    (*e)->name = "example";
    return 0;
// called using:
struct example *the_example;

Little puzzle : why null pointer exception?

By : Mahmud Khan
Date : March 29 2020, 07:55 AM
Hope this helps When you do setValue(null) or setValue("test"), it's explicitly passing in an Object and a String class and they don't match the primitive type long.
However, passing in the object type Long is ok because of Java's autoboxing feature, which automatically converts between the primitive type and its Object wrapper. When you pass in the Long object into anotherValueWrapper's setValue() method, it executes the Long's longValue() method underneath the hood and it would result in NullPointerException if the Long object is null.
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