I'll provide the reasoning steps for generating this patch following the two-step process:

Step 1. Root Cause Analysis:

1. Function parameters:
   - The function takes `pszFileName` as an input parameter, which is a C-style string (char array).

2. Buffer declaration:
   - `szFileName` is declared with a size of `ODBC_FILENAME_MAX + 1`.

3. Vulnerable line analysis:
   - The `strncpy` function is used incorrectly:
     - First argument: Destination buffer (`szFileName`)
     - Second argument: Size of the destination buffer minus 5 (`sizeof(szFileName) - 5`)
     - Third argument: Source string (`pszFileName`)
   - This usage is incorrect because the second argument should be the maximum number of characters to copy, not the size of the destination buffer.

4. Potential vulnerability:
   - This misuse can lead to buffer overflow if `pszFileName` is longer than `sizeof(szFileName) - 5`.
   - The function might write beyond the bounds of `szFileName`, causing memory corruption.

Conclusion:
The vulnerability is caused by incorrect usage of the `strncpy` function, where the size parameter is in the wrong position, potentially leading to buffer overflow.

Step 2. Fixing Strategy:

1. Correct usage of `strncpy`:
   - The second and third arguments of `strncpy` should be swapped to match the correct function signature:
     `strncpy(dest, source, count)`

2. Ensure proper size limitation:
   - Use `sizeof(szFileName) - 5` as the maximum number of characters to copy, leaving space for null termination and potential suffixes.

3. Resulting patch:
```
<         strncpy(szFileName, sizeof(szFileName) - 5, pszFileName);
---
>         strncpy(szFileName, pszFileName, sizeof(szFileName) - 5);
```

This patch corrects the order of arguments in the `strncpy` function call, ensuring that the copy operation is properly bounded by the size of the destination buffer minus 5 characters. This prevents potential buffer overflow and fixes the CWE-787 vulnerability.