is8bit function

Synopsis

$is8bit(<text>)

Technical

Returns the zero-based byte position of the first byte in text with its high bit set, meaning a byte value from 128 through 255. It examines the entire input literally; spaces and quotation marks are part of the text, rather than argument separators or grouping syntax. /xdebug dword does not change this parsing.

This is a byte test, not a Unicode character test or encoding validator. Valid UTF-8 containing a non-ASCII character has high-bit bytes, but invalid UTF-8 and text in other encodings can have them too. Positions count bytes, unlike the Unicode code-point positions returned by $index().

Practical

Use this to locate the first non-ASCII byte in a string. It does not establish whether the string is UTF-8; see $isutf8() for that function's validation behavior. ASCII control bytes have no high bit and therefore do not count as matches.

Returns

A nonnegative byte position when a high-bit byte exists. Returns -1 for a nonempty string containing only bytes below 128, or empty for missing/empty input. There is no diagnostic.

This is not a Boolean result: position zero is a successful match, and -1 is failure. Compare against zero rather than testing numeric truth alone.

Examples

The non-ASCII examples assume the text is encoded as UTF-8.

Source

Registration, literal input scan, high-bit test, and return values: source/functions.c. Integer-string and empty-result macros: include/functions.h.