Issue 0264: graphic characters

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: Clive D.W. Feather <clive@demon.net>, UK C Panel
Date: 2001-09-07
Submitted against: C99
Status: Closed
Converted from: summary-c99.htm, dr_264.htm

Problem

The Standard uses the terms "printing character", "graphic character", and "nongraphic character". The first is discussed in 5.2.2#1 and defined formally in 7.4#3:

[#3] The term printing character refers to a member of a locale-specific set of characters, each of which occupies one printing position on a display device;

A "nongraphic character" is clearly a character which is not a graphic character, but "graphic character" is nowhere defined. It is used only in 5.2.1#3, which requires "the following 29 graphic characters" to be part of the basic character sets, while "nongraphic character" is used in 5.2.2#2 and 6.4.4.4#8 when discussing the \a \b \f \n \r \t and \v escape sequences.

The key questions are:

1. Are the 29 enumerated graphic characters required to be printing characters ?
2. Are isalnum() and isspace() required to be false for them ?
3. Is ispunct() required to be true for them ?

In addition, given that the seven characters corresponding to the escape sequences above are required to be control characters (see 5.2.1#3):

4. Should "nongraphic character" be replaced by "control character" ?

I believe that the answers should be:

1. yes
2. yes;
3. yes in the C locale, but not otherwise;
4. yes.

However, it is not clear that these answers can be derived from the Standard (though if (1) and (2) are "yes", (3) must at least be "yes in the C locale").

Suggested Technical Corrigendum

To address (1): in 5.2.1#3, replace "29 graphic characters" with "29 printing characters".

To address (4): in 5.2.2#2 and 6.4.4.4#8 replace "nongraphic" with "control".

To address (2): append to 5.2.1#4:

A graphical mark character is one of the 29 other printing characters listed above.

in 7.4.1.2#2, insert between the two sentences:

The isalpha function returns false for all graphical mark characters.

and in 7.4.1.10#2, change "characters for which" to "characters which are not graphical mark characters and for which".

Given the above changes, (3) can be derived from the modified Standard.

Comment from WG14 on 2002-03-07:

Committee Response

The referenced sections in the standard only use the term "non-graphic character" in the context of backslash-escape sequences, for which the standard is clear enough, and no changes are needed.