char array object questionsThis issue has been automatically converted from the original issue lists and some formatting may not have been preserved.
Authors: Ron Guilmette, WG14
Date: 1993-12-03
Submitted against: C90
Status: Closed
Converted from: dr.htm, dr_114.html
ANSI/ISO C Defect Report #rfg21:
Subject: Initialization of multi-dimensional char array objects.
a) Does the following code involve usage which requires a diagnostic from a conforming implementation?
b) Does the following code involve usage which renders the code itself not strictly conforming?
char array2[2][5] = { "defghi" }; /* ? */
Background:
Subclause 6.5.7 (Constraints):
There shall be no more initializers in an initializer list than there are objects to be initialized.
Subclause 6.5.7:
An array of character type may be initialized by a character string literal, optionally enclosed in braces.
Subclause 6.5.7 (examples):
... It defines a three-dimensional array object; ...
It appears that many existing compilers seem to feel the the code example shown above violates the “no more initializers” constraint (quoted above) which is given in subclause 6.5.7.
Note however that the entire two-dimensional array object being initialized
consists of exactly 2*5 = 10 individual char objects, whereas the
initializer itself only consists of 7 individual char values (if one counts
the terminating null byte). Thus, it would appear that these existing
implementations are in fact wrong in rejecting the above code, and that such
usage is in fact strictly conforming.
I ask the Committee to unambiguously either confirm or refute that position.
Comment from WG14 on 1997-09-23:
a) Yes, a diagnostic is required.
b) Yes, this renders the program not strictly conforming.
Note that initialization of an array of character type by a string literal is a special case, described in subclause 6.5.7.
The phrases “two-dimensional array” and “three-dimensional array” are merely used for convenience. The Semantics section on array declarators (subclause 6.5.4.2) and the syntax specification in the section on declarations (subclause 6.5.4) clearly show that array types must be declared with one index. Thus, an array which has two indices must be considered an “array of array of type.”
Since this is the case, the Semantics description for initializing aggregates and subaggregates in subclause 6.5.7 applies. This description states
If the initializer of a subaggregate or the first member of the contained union begins with a left brace, the initializers enclosed by that brace and its matching right brace initialize the members of the subaggregate or the first member of the contained union.
Thus, in the example, the string must be applied only to the first element of the two-element array (which is an array of 5 characters). Since the initializer contains 6 characters, it violates the constraint of the same section which states:
There shall be no more initializers in an initializer list than there are objects to be initialized.