在我编写的一个小程序中使用 64 位整数时，我看到了一些非常奇怪的行为。我的程序执行以下操作...
- 创建 2D long long int 数组（X 乘 Y）
- 初始化从 0 到 X*Y -1 的所有数组索引值
- 将第一行和第一列索引设置为值 1
这是我的程序的代码（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);
}
在编译和运行代码之后，我得到了这个输出
$ 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.
在多次检查我的逻辑并且没有发现任何错误之后，我决定制作另一个版本的程序，只是用 int 替换“long long int”变量。
这段代码粘贴在下面（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);
}
只是为了证明我在这两个程序之间所做的唯一区别是将“long long int”变量替换为“int”（并相应地更改 printf 调用），这是两个源文件之间的差异
$ 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++)
$
然而，当这个版本的代码运行时，我得到了我期望的输出！
$ 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
$
正如我所展示的，我使用 -m64 标志编译了这两个程序，并且我的笔记本电脑中有一个 i7 处理器，它是一个 64 位处理器。我还尝试了将所有“long long int”实例替换为“long int”的程序版本，以及将所有“long long int”替换为“int64_t”的另一个版本，但我得到的输出不正确也适用于这两个版本。
任何人都知道为什么我在这里看到行为有所不同？