Bug #18956: Kernel#sprintf - %c handles negative Integer argument in a confusing way

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 3.0.3
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[andrykonchin (Andrew Konchin)]

Integer argument for %c means a character codepoint.

I've noticed two outcomes when argument is negative:

• exception
• broken/incorrect string

When exception is raised - its message a bit misleading and confusing:

sprintf("%c", -1000)
# => invalid character (ArgumentError)

sprintf("%c".encode('ascii'), -1)
# => 4294967295 out of char range (RangeError)

invalid character means there is a character, but actual argument is a codepoint. 4294967295 out of char range is about codepoint, but it mentions 4294967295 instead of actual argument -1.

sprintf("%c", -1)
# => "\xFF"

In this case no exception is risen but the string is not valid:

sprintf("%c", -1).codepoints
# => invalid byte sequence in UTF-8 (ArgumentError)
sprintf("%c", -1).valid_encoding?
# => false

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[mame (Yusuke Endoh)]

@naruse (Yui NARUSE), @nobu (Nobuyoshi Nakada), and @matz (Yukihiro Matsumoto) agreed that a negative integer to %c should raise an explicit exception.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|d2483393cbcb4dcfa0000fa8166bb7fa7ed9f7b4.

---

[Bug #18956] Negative codepoints are invalid characters