Defect Report #019

Submission Date: 10 Dec 92
Submittor: WG14
Source: X3J11/91-014 (Richard Wiersma)
Question 1
Subclause states that ``the isgraph function tests for any printing character except space.'' Subclause states that ``the isprint function tests for any printing character including space.''
The third paragraph of subclause 7.3 defines the term printing character as ``a member of an implementation-defined set of characters, each of which occupies one printing position on a display device.''
Subclause 5.2.1 defines the source and execution character sets and provides a list of characters which must be contained in both sets.
Question for interpretation: Are the isprint and isgraph functions required to return a non-zero value for all of the characters defined in subclause 5.2.1?
A scenario for use of isprint/isgraph that depends on the interpretation is: A developer may wish to use these functions to determine whether a particular character can be displayed as itself (e.g., whether a square bracket is actually displayed as a square bracket). This could be useful for formatting output in a device-independent manner, since the application could substitute some other character for ones that do not print ``correctly.''
If isprint and isgraph are required to return non-zero for all characters in subclause 5.2.1, developers cannot use them for this purpose.
This problem has occurred in a real implementation. The most commonly used terminals and printers for IBM System/370 computers do not support all of the characters listed in subclause 5.2.1. For example, most IBM printers and terminals do not print the square brackets.
The SAS/C implementation of isprint and isgraph assumes that subclause 7.3 controls the behavior of these functions, and returns non-zero only for those characters that print ``correctly.'' The Plum Hall test suite, however, assumes that isprint and isgraph return non-zero for all characters listed in subclause 5.2.1.
Subclause 7.3, page 102, line 8 says that printing character is implementation-defined. In particular, the value (zero or non-zero) of isprint('[') is implementation-defined, even in the "C" locale.
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