Defect Report #107

Submission Date: 03 Dec 93
Submittor: WG14
Source: Ron Guilmette
Question
ANSI/ISO C Defect report #rfg14:
Subclause 7.2.1.1 (Synopsis) says:

#include <assert.h> void assert(int expression);

This synopsis raises several related questions.
a) May a strictly conforming program contain code which includes an invocation of the assert macro for an expression whose type is not directly convertible to type int? (See examples below.)
b) Must a conforming implementation issue diagnostics for any and all attempts to invoke the assert macro for an expression having some type which is not directly convertible to type int?
Examples:
#include <assert.h> char *cp; void (*fp) (); struct S { int member; } obj; void example () { assert (cp); /* conforming code? diagnostic required? */ assert (fp); /* conforming code? diagnostic required? */ assert (obj); /* conforming code? diagnostic required? */ }
c) Must a conforming implementation convert the value yielded by the expression given in an invocation of the assert macro to type int before checking to see if it compares equal to zero?
Example:
#include <assert.h> void example () { assert (0.1); /* must this casue an abort? must it NOT? */ }
Response
a) The definition of assert depends on the NDEBUG macro. The Synopsis provides information on how an implementation may use the parameter. If NDEBUG is defined as a macro, the parameter is not used and hence cannot cause undefined behavior. If NDEBUG is not defined as a macro, the implementation may rely on the parameter having type int. Passing a non-int argument in such a context will render the translation unit not strictly conforming.
b) If NDEBUG is defined as a macro, the parameter is not used and no diagnostic should occur. Otherwise, a violation of this requirement results in undefined behavior, which does not require a diagnostic.
c) No.
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