I'm seeing some very strange behavior when using 64 bit integers in a little program I've written. My program does the following...
- create 2D long long int array (X by Y)
- Initialize all array indice values from 0 to X*Y -1
- Set the first row and first column indices to have value 1
Here is the code for my program (numWaysXY_iterative.cc)
#include<stdio.h>
#include<iostream>
using namespace std;
void printMap(int X, int Y, long long int **map)
{
printf("printing map(%d, %d)...\n\n", X, Y);
for(long long int i = 0; i < Y; i++)
{
for(long long int j = 0; j < X; j++)
{
printf("(%lld, %lld) value: %lld\t", j, i, map[j][i]);
}
printf("\n");
}
printf("Finished Printing map\n");
}
long long int numWaysXY_iterative(long long int X, long long int Y)
{
long long int **map = new long long int*[X];
long long int value = 0;
for(long long int i = 0; i < X; i++)
{
map[i] = new long long int(Y);
for(long long int j = 0; j < Y; j++)
{
printf("i: %lld, j: %lld, value: %lld\n", i, j, value);
map[i][j] = value;
value++;
}
}
//debugging - print map
printMap(X,Y, map);
//initialize first row and first column entries to 1
for(long long int i = 0; i < X; i++)
{
map[i][0] = 1;
}
for(long long int j = 0; j < Y; j++)
{
map[0][j] = 1;
}
//debugging - print map
printMap(X,Y, map);
/*
for(int i = 0; i < X, i++)
{
for(int j = 0; j > Y, j++)
{
if
}
}
*/
return map[X-1][Y-1];
}
int main()
{
(void) numWaysXY_iterative(5,3);
}
Afer compiling and running the code, I get this output
$ g++ my_solution/numWaysXY_iterative/numWaysXY_iterative.cc -m64 -o executables/numWaysXY_iterative
$
$
$
$ ./executables/numWaysXY_iterative
i: 0, j: 0, value: 0
i: 0, j: 1, value: 1
i: 0, j: 2, value: 2
i: 1, j: 0, value: 3
i: 1, j: 1, value: 4
i: 1, j: 2, value: 5
i: 2, j: 0, value: 6
i: 2, j: 1, value: 7
i: 2, j: 2, value: 8
i: 3, j: 0, value: 9
i: 3, j: 1, value: 10
i: 3, j: 2, value: 11
i: 4, j: 0, value: 12
i: 4, j: 1, value: 13
i: 4, j: 2, value: 14
printing map(5, 3)...
(0, 0) value: 0 (1, 0) value: 3 (2, 0) value: 6 (3, 0) value: 9 (4, 0) value: 12
(0, 1) value: 1 (1, 1) value: 4 (2, 1) value: 7 (3, 1) value: 10 (4, 1) value: 13
(0, 2) value: 3 (1, 2) value: 6 (2, 2) value: 9 (3, 2) value: 12 (4, 2) value: 14
Finished Printing map
printing map(5, 3)...
(0, 0) value: 1 (1, 0) value: 1 (2, 0) value: 1 (3, 0) value: 1 (4, 0) value: 1
(0, 1) value: 1 (1, 1) value: 4 (2, 1) value: 7 (3, 1) value: 10 (4, 1) value: 13
(0, 2) value: 1 (1, 2) value: 1 (2, 2) value: 1 (3, 2) value: 1 (4, 2) value: 14
Finished Printing map
Problems:
1. After initializing the values of the array in lines 26 - 35, even though the value
variable is strictly increasing, and each array indice is supposedly getting a unique
value assigned to it, this is not being reflected in the array. You can see that
map[0][2] == map[1][0] for example.
2. I'm setting the first row and first column array elements to have the value 1 in lines
40 - 48, but again this is not reflected when the array is printed out. Instead it
seems that the first row, first column, and all elements in the last row besides the
last are being set to 1.
After going over my logic several times and not seeing anything wrong, I decided to make another version of the program, just replacing the "long long int" variables with int instead.
This code is pasted below (debug_numWaysXY_iterative.cc)
#include<stdio.h>
#include<iostream>
using namespace std;
void printMap(int X, int Y, int **map)
{
printf("printing map(%d, %d)...\n\n", X, Y);
for(int i = 0; i < Y; i++)
{
for(int j = 0; j < X; j++)
{
printf("(%d, %d) value: %d\t", j, i, map[j][i]);
}
printf("\n");
}
printf("Finished Printing map\n");
}
int numWaysXY_iterative(int X, int Y)
{
int **map = new int*[X];
int value = 0;
for(int i = 0; i < X; i++)
{
map[i] = new int(Y);
for(int j = 0; j < Y; j++)
{
printf("i: %d, j: %d, value: %d\n", i, j, value);
map[i][j] = value;
value++;
}
}
//debugging - print map
printMap(X,Y, map);
//initialize first row and first column entries to 1
for(int i = 0; i < X; i++)
{
map[i][0] = 1;
}
for(int j = 0; j < Y; j++)
{
map[0][j] = 1;
}
//debugging - print map
printMap(X,Y, map);
/*
for(int i = 0; i < X, i++)
{
for(int j = 0; j > Y, j++)
{
if
}
}
*/
return map[X-1][Y-1];
}
int main()
{
(void) numWaysXY_iterative(5,3);
}
Just to prove that the only difference I made between these 2 programs is replacing the "long long int" variables with "int" (and changing the printf calls accordingly), here is the diff between the 2 source files
$ diff my_solution/numWaysXY_iterative/numWaysXY_iterative.cc my_solution/numWaysXY_iterative/debug_numWaysXY_iterative.cc
6c6
< void printMap(int X, int Y, long long int **map)
---
> void printMap(int X, int Y, int **map)
9c9
< for(long long int i = 0; i < Y; i++)
---
> for(int i = 0; i < Y; i++)
11c11
< for(long long int j = 0; j < X; j++)
---
> for(int j = 0; j < X; j++)
13c13
< printf("(%lld, %lld) value: %lld\t", j, i, map[j][i]);
---
> printf("(%d, %d) value: %d\t", j, i, map[j][i]);
20c20
< long long int numWaysXY_iterative(long long int X, long long int Y)
---
> int numWaysXY_iterative(int X, int Y)
22c22
< long long int **map = new long long int*[X];
---
> int **map = new int*[X];
24c24
< long long int value = 0;
---
> int value = 0;
26c26
< for(long long int i = 0; i < X; i++)
---
> for(int i = 0; i < X; i++)
28,29c28,29
< map[i] = new long long int(Y);
< for(long long int j = 0; j < Y; j++)
---
> map[i] = new int(Y);
> for(int j = 0; j < Y; j++)
31c31
< printf("i: %lld, j: %lld, value: %lld\n", i, j, value);
---
> printf("i: %d, j: %d, value: %d\n", i, j, value);
41c41
< for(long long int i = 0; i < X; i++)
---
> for(int i = 0; i < X; i++)
45c45
< for(long long int j = 0; j < Y; j++)
---
> for(int j = 0; j < Y; j++)
$
However when this version of the code runs, I get output that I expect!!
$ g++ my_solution/numWaysXY_iterative/debug_numWaysXY_iterative.cc -m64 -o executables/debug_numWaysXY_iterative
$
$
$
$ ./executables/debug_numWaysXY_iterative
i: 0, j: 0, value: 0
i: 0, j: 1, value: 1
i: 0, j: 2, value: 2
i: 1, j: 0, value: 3
i: 1, j: 1, value: 4
i: 1, j: 2, value: 5
i: 2, j: 0, value: 6
i: 2, j: 1, value: 7
i: 2, j: 2, value: 8
i: 3, j: 0, value: 9
i: 3, j: 1, value: 10
i: 3, j: 2, value: 11
i: 4, j: 0, value: 12
i: 4, j: 1, value: 13
i: 4, j: 2, value: 14
printing map(5, 3)...
(0, 0) value: 0 (1, 0) value: 3 (2, 0) value: 6 (3, 0) value: 9 (4, 0) value: 12
(0, 1) value: 1 (1, 1) value: 4 (2, 1) value: 7 (3, 1) value: 10 (4, 1) value: 13
(0, 2) value: 2 (1, 2) value: 5 (2, 2) value: 8 (3, 2) value: 11 (4, 2) value: 14
Finished Printing map
printing map(5, 3)...
(0, 0) value: 1 (1, 0) value: 1 (2, 0) value: 1 (3, 0) value: 1 (4, 0) value: 1
(0, 1) value: 1 (1, 1) value: 4 (2, 1) value: 7 (3, 1) value: 10 (4, 1) value: 13
(0, 2) value: 1 (1, 2) value: 5 (2, 2) value: 8 (3, 2) value: 11 (4, 2) value: 14
Finished Printing map
$
As I've shown I compiled both programs with -m64 flag, and I have a i7 processor in my laptop, which is a 64 bit processor. I've also tried versions of my program with all instances of "long long int" replaced with "long int" and another version where I've replaced all "long long int" with "int64_t", and I'm getting incorrect output for both of those versions too.
Anyone have any idea why I'm seeing a difference in behavior here?
