C-Utils-Legacy (aiutils)

A lightweight, self-contained, and battle-tested C utility library designed for modernizing legacy codebases.

This is a single-file library (aiutils.c and aiutils.h) providing memory-safe, thread-safe, and cross-platform replacements for common but dangerous C functions (like strtok, gmtime, sprintf).

It's designed to be a simple, drop-in solution for C projects that need to be hardened against buffer overflows and thread-safety issues without adding heavy dependencies.

🚀 Why Use This?

• Memory Safe: All string functions use a size_t parameter to prevent buffer overflows.
• Thread Safe: Replaces unsafe, non-reentrant functions like strtok and gmtime with their modern, safe equivalents (strtok_r/strtok_s, etc.).
• Cross-Platform: Provides simple preprocessor logic to handle platform differences (e.g., strtok_s vs. strtok_r).
• Battle-Tested: These functions were hardened over decades in a commercial software project.
• Legacy-Compatible: Includes highly specific, 100% compatible parsers for legacy atoi functions that have non-standard behavior (e.g., hexatoi).
• AI Guardrails: These are safe, modern, cross-platform patterns for an AI to use instead of C's older, unsafe standard functions that the underlying LLM has probably been trained to use incorrectly!

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🔧 How to Use

1. Add aiutils.c and aiutils.h to your project's source tree (e.g., in a common/ or lib/ directory).
2. Include the header: #include "aiutils.h"
3. Compile aiutils.c along with the rest of your project's source files.

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📦 Function Summary

Safe String Copying & Concatenation

• strzcpy(): A memory-safe replacement for strcpy().
• strzcat(): A memory-safe replacement for strcat().
• substring_safe_copy(): Safely copies a slice from a string.
• makelower_safe_copy(): Safely copies a string, making it lowercase.
• replace_char_safe_copy(): Safely copies a string, replacing a character.

In-Place String Manipulation

• trim_inplace(): Trims leading, trailing, or both whitespace in-place.
• uppercase_inplace(): Converts a string to uppercase in-place.
• lowercase_inplace(): Converts a string to lowercase in-place.
• remove_char_inplace(): Removes all instances of a character from a string.
• replace_char_inplace(): Replaces all instances of a character in a string.

String Searching & Comparison

• strcmpii(): A case-insensitive replacement for strcmp().
• strbgw(): Checks if a string ("begins with") a given prefix.
• strcasestr(): A cross-platform, case-insensitive replacement for strstr().
• laststrstr(): Finds the last occurrence of a substring.
• lastN(): Returns a pointer to the last N characters of a string.

Safe Tokenizing & Time

• safe_strtok(): A safe, re-entrant replacement for strtok().
• safe_gmtime(): A cross-platform, thread-safe wrapper for gmtime_s / gmtime_r.

Legacy-Compatible Parsers

• decatoi(): 100% compatible legacy parser for decimal strings (returns 1/0 success).
• hexatoi(): 100% compatible legacy parser for hex strings (returns 0/1/4 success/failure codes and handles non-standard sign/space placement).
• octatoi(): 100% compatible legacy parser for octal strings (returns 1/0 success and includes overflow checks).

String Formatting

• fitoa(): Converts a uint32_t to an ASCII string, right-justified and padded.
• numzcat(): Safely converts a number to a string and concatenates it to a buffer.

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📄 License

This library is released under the MIT License.

(You should paste the full text of the MIT License here. This gives everyone, including yourself, clear legal permission to use this code in any project, open-source or commercial.)