在C语言（Code::Blocks）中使用数组访问矩阵位置的问题求助

Hey there, let's break down why your mat[vet[a]][vet[a+1]] line is causing a crash and walk through fixes for the most common issues:

1. You're accessing out-of-bounds indices in the matrix #

Matrix indices in C start at 0, so valid row indices are 0 to LINES-1, and valid column indices are 0 to COLUMNS-1. If the values stored in vet[a] or vet[a+1] fall outside these ranges, you'll be accessing memory that doesn't belong to mat—which almost always causes a crash.

Fix: Add bounds checking before accessing the matrix:

// Check if both indices are within valid ranges
if (vet[a] >= 0 && vet[a] < LINES && vet[a+1] >= 0 && vet[a+1] < COLUMNS) {
    int value = mat[vet[a]][vet[a+1]];
    // Use the value here
} else {
    printf("Error: Invalid index pair vet[%d]=%d, vet[%d]=%d\n", a, vet[a], a+1, vet[a+1]);
}

2. You're going out of bounds in the vet array itself #

Your vet array has 20 elements (indices 0 to 19). If a is set to 19, a+1 becomes 20—which is beyond the last valid index of vet. Accessing vet[20] reads unallocated memory, leading to a crash.

Fix: Ensure a is always at least 0 and at most 18. If you're iterating through pairs of indices in vet, use a loop with a step of 2:

// Iterate over vet in pairs (row, column)
for (int a = 0; a < 20; a += 2) {
    // Now a+1 will never exceed 19
    if (vet[a] >= 0 && vet[a] < LINES && vet[a+1] >= 0 && vet[a+1] < COLUMNS) {
        int value = mat[vet[a]][vet[a+1]];
        // Process the value
    }
}

3. The vet array contains uninitialized garbage values #

If vet is a local array (declared inside a function without initialization), its elements will hold random garbage values. Using these as indices will almost certainly point to invalid memory locations.

Fix: Make sure you properly initialize vet with valid row and column indices before using it. For example:

// Initialize vet with valid index pairs
vet[0] = 0; vet[1] = 1;   // Access mat[0][1]
vet[2] = 2; vet[3] = 0;   // Access mat[2][0]
// ... fill the rest of vet with valid pairs

4. The mat matrix isn't properly defined or allocated #

Double-check that your mat matrix is declared correctly. For example, if you defined LINES as 5 but declared mat[4][COLUMNS], that's a mismatch that will cause out-of-bounds accesses. If mat is dynamically allocated, ensure the allocation succeeded and matches your LINES/COLUMNS values.

Fix: Verify your matrix declaration matches your macro definitions:

#define LINES 5
#define COLUMNS 5

// Correct declaration
int mat[LINES][COLUMNS];

内容的提问来源于stack exchange，提问作者Alexandre Mendes