isxdigitA

isxdigitA is a variant of the C standard library function isxdigit that is used in some C runtime libraries to operate on ANSI (single-byte) character input. The A suffix indicates that the function targets the ANSI character set, as opposed to wide-character versions that operate on wchar_t input (often named isxdigitW). In practice, isxdigitA determines whether a given character represents a hexadecimal digit.

Prototype and behavior

- Typical signature: int isxdigitA(int ch);

- Parameter ch must be representable as an unsigned char or be the value EOF. The function returns a nonzero value if ch is a hexadecimal digit, i.e., one of the characters '0' through '9', 'a' through 'f', or 'A' through 'F'. Otherwise it returns zero.

- The classification usually follows the same logic as the standard isxdigit, but isxdigitA is explicitly intended for ANSI/ASCII input rather than wide characters. In many implementations, the functional result is independent of locale for ASCII-compatible inputs, though behavior for non-ASCII code pages may vary.

Typical usage and portability

- isxdigitA is commonly provided in environments that offer separate A and W variants for CRT functions, such as Windows’ C runtime. Some codebases may map isxdigit to isxdigitA or isxdigitW via macros depending on whether ANSI or wide-character processing is in use.

- As with other ctype-style functions, the result is undefined if ch is not representable as an unsigned char and not equal to EOF.

Notes

- When writing portable code, prefer the standard isxdigit function from <ctype.h> and ensure the input is cast to unsigned char as needed. The A variant is mostly relevant in ecosystems that distinguish ANSI and wide-character interfaces and where explicit ANSI handling is required.