Defect Report #143

Submission Date: 23 Feb 95
Submittor: BSI
Source: Clive D.W. Feather
Question
Submitted to BSI by Clive D.W. Feather [email protected].
In this Defect Report, identifiers lexically identical to those declared in standard headers refer to the identifiers declared in those standard headers, whether or not the header is explicitly mentioned.
This Defect Report has been prepared with considerable help from Mark Brader, Jutta Degener, Ronald Guilmette, and a person whose employment conditions require anonymity. However, except where stated, opinions expressed or implied should not be assumed to be those of any person other than myself.
Defect Report UK 027: fopen modes
[BSI characterize this issue as minor.]
The definition of file opening modes is self-contradictory.
Subclause 7.9.5.3 reads in part:

The argument mode points to a string beginning with one of the following sequences:

and then lists all of r, r+, rb, and rb+ or r+b, with different meanings. Obviously, it is possible for a string to begin with up to three of these simultaneously, and thus the quoted text is contradictory.
Also, the wording is confusing since it can easily be misread as "beginning with exactly one of the following sequences," which would prohibit those of the specified modes that are longer than one character.
Suggested Technical Corrigendum:
Change the quoted text to:

The mode is determined by the longest match of the following sequences to the initial characters of the string pointed to by the argument mode; at least the initial character shall match.

Suggested Future Change
The current C Standard has correct meaning, but the wording could be clearer. We suggest the following change for the revised C Standard:

The argument mode points to a string. The mode is determined by the string's longest initial match to the following sequences; at least the initial character shall match:

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