Conformance
4. Conformance
1 In this International Standard, ‘‘shall’’ is to be interpreted as a requirement on an
implementation or on a program; conversely, ‘‘shall not’’ is to be interpreted as a
prohibition.
2 If a ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint is violated, the
behavior is undefined. Undefined behavior is otherwise indicated in this International
Standard by the words ‘‘undefined behavior’’ or by the omission of any explicit definition
of behavior. There is no difference in emphasis among these three; they all describe
‘‘behavior that is undefined’’.
3 A program that is correct in all other aspects, operating on correct data, containing
unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
4 The implementation shall not successfully translate a preprocessing translation unit
containing a #error preprocessing directive unless it is part of a group skipped by
conditional inclusion.
5 Astrictly conforming program shall use only those features of the language and library
specified in this International Standard.2) It shall not produce output dependent on any
unspecified, undefined, or implementation-defined behavior, and shall not exceed any
minimum implementation limit.
6 The two forms of conforming implementation are hosted and freestanding. A conforming
hosted implementation shall accept any strictly conforming program. A conforming
freestanding implementation shall accept any strictly conforming program that does not
use complex types and in which the use of the features specified in the library clause
(clause 7) is confined to the contents of the standard headers <float.h>,
<iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, and
<stdint.h>. A conforming implementation may have extensions (including additional
library functions), provided they do not alter the behavior of any strictly conforming
program.3)
2) A strictly conforming program can use conditional features (such as those in annex F) provided the
use is guarded by a #ifdef directive with the appropriate macro. For example:
#ifdef _ _STDC_IEC_559_ _ /* FE_UPWARD defined */
/* ... */
fesetround(FE_UPWARD);
/* ... */
#endif
3) This implies that a conforming implementation reserves no identifiers other than those explicitly
reserved in this International Standard.
7 Aconforming program is one that is acceptable to a conforming implementation.4)
8 An implementation shall be accompanied by a document that defines all implementationdefined
and locale-specific characteristics and all extensions.
Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
(7.9), sizes of integer types <limits.h> (7.10), variable arguments <stdarg.h>
(7.15), boolean type and values <stdbool.h> (7.16), common definitions
<stddef.h> (7.17), integer types <stdint.h> (7.18).
4) Strictly conforming programs are intended to be maximally portable among conforming
implementations. Conforming programs may depend upon nonportable features of a conforming
implementation.