Check whether files could be opened before writing; resolves #542

[liuzicheng1987]

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[gemini-code-assist]

Summary of Changes

Hello @liuzicheng1987, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the reliability of file writing operations by integrating explicit checks for successful file stream opening. By verifying that files can be accessed for writing before proceeding, the changes prevent potential runtime errors and provide clearer feedback to users when file system issues arise, directly addressing a reported issue.

Highlights

• Robust File Writing: Introduced explicit checks to ensure output file streams are successfully opened before attempting to write data, enhancing the robustness of file operations.
• Error Handling for save_bytes: The save_bytes function now verifies the ofstream object's status immediately after construction, returning an error if the file could not be opened.
• Error Handling for save_string: The save_string function now includes an is_open() check. However, this check is currently placed before the outfile.open(_fname) call, which will cause it to always return an error for a default-constructed ofstream.

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[gemini-code-assist]

Code Review

This pull request correctly adds a check in save_bytes.hpp to ensure the file can be opened before writing. However, a critical logical error has been introduced in save_string.hpp. The check for whether the file is open is performed before the file is actually opened, which will cause the function to always fail. I have provided a review comment with a suggested fix for this issue.