RegError is a standard POSIX function used in C and C++ programming to convert numeric error codes generated by regular expression (regex) operations into human-readable strings. While regex is a powerful tool for pattern matching, its implementation often involves complex underlying engines that return cryptic integer codes when something goes wrong—such as an invalid pattern or a memory failure. How RegError Works
In the standard workflow of the regcomp() (which compiles a pattern) and regexec() (which executes it) return an integer status. If this status is non-zero, an error has occurred. RegError then steps in to translate that number into a descriptive message. Description Purpose Maps error codes to printable strings. Input
An error code (errcode) and the compiled regex structure (preg). Output
A descriptive string (e.g., “Invalid range end”) and the size of the required buffer. Portability
Defined by POSIX 1003.1, making it available on most Unix-like systems, including Linux, BSD, and AIX. Common Error Messages
When debugging regex, you might encounter specific error strings generated through this function, including: REG_BADPAT: The regular expression itself is invalid. REG_EBRACK: Imbalanced square brackets []. REG_EPAREN: Imbalanced parentheses ().
REG_ESPACE: The system ran out of memory while attempting to process the pattern.
REG_NOMATCH: The pattern simply did not find a match in the provided text. Implementation Details
To use regerror safely, developers typically call it twice. The regerror() — Return Error Message – IBM documentation notes that if the provided buffer is too small, the message is truncated. Consequently, a common pattern involves first calling the function with a zero-length buffer to find the required size, then allocating that memory and calling it again to retrieve the full message.
For more detailed technical specifications, developers can refer to the POSIX regex functions – Linux man page or IBM’s regerror subroutine guide.
If you’re working on a project, would you like a code example in C showing how to handle these errors, or do you need help debugging a specific regex pattern? regerror() — Return error message – IBM