common: introduce bt_g_array_index
[babeltrace.git] / src / common / macros.h
1 /*
2 * SPDX-License-Identifier: MIT
3 *
4 * Copyright 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 */
6
7 #ifndef _BABELTRACE_INTERNAL_H
8 #define _BABELTRACE_INTERNAL_H
9
10 #ifdef __cplusplus
11 extern "C" {
12 #endif
13
14 #ifdef __cplusplus
15 #define BT_EXTERN_C extern "C"
16 #else
17 #define BT_EXTERN_C
18 #endif
19
20 #define bt_max_t(type, a, b) \
21 ((type) (a) > (type) (b) ? (type) (a) : (type) (b))
22
23 /*
24 * BT_EXPORT: set the visibility for exported functions.
25 */
26 #if defined(_WIN32) || defined(__CYGWIN__)
27 #define BT_EXPORT
28 #else
29 #define BT_EXPORT __attribute__((visibility("default")))
30 #endif
31
32 /*
33 * Yield `ref`'s value while setting `ref` to NULL.
34 *
35 * This can be used to give a strong reference to a callee:
36 *
37 * add_foo_to_list(list, BT_MOVE_REF(foo));
38 *
39 * or in a simple assignment:
40 *
41 * my_struct->foo = BT_MOVE_REF(foo);
42 *
43 * When moving a reference in a function call, the reference is given to the
44 * callee even if that function call fails, so make sure the called function
45 * is written accordingly.
46 */
47
48 #define BT_MOVE_REF(ref) \
49 ({ \
50 __typeof__(ref) _ref = ref; \
51 ref = NULL; \
52 _ref; \
53 })
54
55 /* Wrapper for g_array_index that adds bound checking. */
56 #define bt_g_array_index(a, t, i) \
57 g_array_index((a), t, ({ BT_ASSERT_DBG((i) < (a)->len); (i); }))
58
59 /*
60 * Copied from:
61 * <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
62 *
63 * * sizeof() ensures that the expression is not evaluated at all, so
64 * its side-effects don't happen. That is to be consistent with the
65 * usual behaviour of debug-only constructs, such as assert().
66 *
67 * * `((_expr), 0)` uses the comma operator to swallow the actual type
68 * of `(_expr)`. This is to prevent VLAs from triggering evaluation.
69 *
70 * * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
71 * no "unused value" warning appears.
72 */
73
74 #define BT_USE_EXPR(_expr) ((void) sizeof((void) (_expr), 0))
75 #define BT_USE_EXPR2(_expr1, _expr2) \
76 ((void) sizeof((void) (_expr1), (void) (_expr2), 0))
77 #define BT_USE_EXPR3(_expr1, _expr2, _expr3) \
78 ((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
79 #define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4) \
80 ((void) sizeof((void) (_expr1), (void) (_expr2), \
81 (void) (_expr3), (void) (_expr4), 0))
82 #define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5) \
83 ((void) sizeof((void) (_expr1), (void) (_expr2), \
84 (void) (_expr3), (void) (_expr4), (void) (_expr5), 0))
85
86 #if defined __clang__
87 # if __has_warning("-Wunused-but-set-variable")
88 # define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE \
89 _Pragma("GCC diagnostic ignored \"-Wunused-but-set-variable\"")
90 # endif
91 #endif
92
93 #if !defined BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
94 # define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
95 #endif
96
97 #ifdef __cplusplus
98 }
99 #endif
100
101 #endif
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