1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
@c GNU verify module documentation
@c Copyright (C) 2006, 2009 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3
@c or any later version published by the Free Software Foundation;
@c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
@c Texts. A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.
@node Compile-time Assertions
@section Compile-time Assertions
@cindex assertion
@findex verify
@findex verify_true
The @samp{verify} module supports compile-time tests, as opposed to
the standard @file{assert.h} header which supports only runtime tests.
Since the tests occur at compile-time, they are more reliable, and
they require no runtime overhead.
This module provides a header file @file{verify.h} that defines two
macros: @code{verify (@var{EXPRESSION})} and @code{verify_true
(@var{EXPRESSION})}. Both accept an integer constant expression
argument and verify that it is nonzero. If not, a compile-time error
results.
@code{verify (@var{EXPRESSION});} is a declaration; it can occur
outside of functions. In contrast, @code{verify_true
(@var{EXPRESSION})} is an integer constant expression that always
evaluates to 1; it can be used in macros that expand to
expressions.
@var{EXPRESSION} should be an integer constant expression in the sense
of the C standard. Its leaf operands should be integer, enumeration,
or character constants; or @code{sizeof} expressions that return
constants; or floating constants that are the immediate operands of
casts. Outside a @code{sizeof} subexpression, @var{EXPRESSION} should
not contain any assignments, function calls, comma operators, casts to
non-integer types, or subexpressions whose values are outside the
representable ranges for their types. If @var{EXPRESSION} is not an
integer constant expression, then a compiler might reject a usage like
@samp{verify (@var{EXPRESSION});} even when @var{EXPRESSION} is
nonzero.
Here are some example uses.
@example
#include <verify.h>
#include <limits.h>
#include <time.h>
/* Verify that time_t is an integer type. */
verify ((time_t) 1.5 == 1);
/* Verify that time_t is at least as wide as int. */
verify (INT_MIN == (time_t) INT_MIN);
verify (INT_MAX == (time_t) INT_MAX);
/* Verify that time_t is signed. */
verify ((time_t) -1 < 0);
/* Verify that time_t uses two's complement representation. */
verify (~ (time_t) -1 == 0);
/* Return the maximum value of the integer type T,
verifying that T is an unsigned integer type. */
#define MAX_UNSIGNED_VAL_WITH_COMMA(t) \
(verify_true (0 < (T) -1), (T) -1)
/* Same as MAX_UNSIGNED_VAL_WITH_COMMA,
but expand to an integer constant expression,
which cannot contain a comma operator.
The cast to (T) is outside the conditional expression
so that the result is of type T
even when T is narrower than unsigned int. */
#define MAX_UNSIGNED_VAL(t) ((T) \
((T) (verify_true (0 < (T) -1) ? -1 : 0))
@end example
|
