以下函数用于找到整数矩阵matrix中，元素之和最大的n行m列的子矩阵的元素之和。请指出程序代码中错误的地方（问题不止一处，请尽量找出所有你认为错误的地方），并在不新增代码行的情况下将问题修复。
1 int maxSubmatrixSum(std::vector<std::vector<int>> matrix,
2 int n, int m) {
3 int base_sum;
4 for (int i = 0; i < n; i++){
5 for (int j = 0; j < m; j++){
6 base_sum += matrix[i][j];
7 }
8 }
9 int result = 0;
10 for (int i = 0; i + n < matrix.size(); i++) {
11 if(i > 0){
12 for (int y = 0; y < m; y++){
13 base_sum += matrix[i + n][y] - matrix[i - 1][y];
14 }
15 }
16 int real_sum = base_sum;
17 if (real_sum > result) {
18 result = real_sum;
19 }
20 for (int j = 0; j + m < matrix.size(); j++) {
21 for (int x = 0; x < n; x++) {
22 real_sum += matrix[x][j + m] - matrix[x][j - 1];
23 }
24 if (real_sum > result) {
25 result = real_sum;
26 }
27 }
28 }
29 return result;
30 }
2 int n, int m) {
3 int base_sum;
4 for (int i = 0; i < n; i++){
5 for (int j = 0; j < m; j++){
6 base_sum += matrix[i][j];
7 }
8 }
9 int result = 0;
10 for (int i = 0; i + n < matrix.size(); i++) {
11 if(i > 0){
12 for (int y = 0; y < m; y++){
13 base_sum += matrix[i + n][y] - matrix[i - 1][y];
14 }
15 }
16 int real_sum = base_sum;
17 if (real_sum > result) {
18 result = real_sum;
19 }
20 for (int j = 0; j + m < matrix.size(); j++) {
21 for (int x = 0; x < n; x++) {
22 real_sum += matrix[x][j + m] - matrix[x][j - 1];
23 }
24 if (real_sum > result) {
25 result = real_sum;
26 }
27 }
28 }
29 return result;
30 }
