Defect Report #147

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 031: Sequence points in library functions
There is no requirement for a sequence point to occur within a library function, since it might not be written in C. Consider the following code:
#include <string.h> char s[10]; /* ... */ (strcpy)(s, "Testing") [0] = 'X'; Any function written in C must have a sequence point after the last full expression evaluated (which will be the returned value if there is one), so if strcpy were a C function, the assigning of 'T' to s[0] would be completed before the call returned.
However, since library functions might not be written in C, they might not have such a sequence point. If not, then the above statement is in breach of the requirements of the second paragraph of subclause 6.3.
Suggested Technical Corrigendum:
Add to the end of subclause 7.1.7:
There is a sequence point immediately before a library function returns.
Add to the end of annex C:

Immediately before a library function returns (7.1.7).
Add a reference to 7.1.7 in the Forward References of 5.1.2.3, and in the relevant Index entry.
Response
We agree that the current wording does not make this clear. The next revision of the C Standard will clarify that every function return is a sequence point. The suggested changes will be used.
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