Tor 0.4.9.0-alpha-dev
ctassert.h
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1/* Copyright (c) 2018 The Tor Project, Inc. */
2/* See LICENSE for licensing information */
3
4/**
5 * \file ctassert.h
6 *
7 * \brief Compile-time assertions: CTASSERT(expression).
8 */
9
10#ifndef TOR_CTASSERT_H
11#define TOR_CTASSERT_H
12
14
15/**
16 * CTASSERT(expression)
17 *
18 * Trigger a compiler error if expression is false.
19 */
20#if __STDC_VERSION__ >= 201112L
21
22/* If C11 is available, just use _Static_assert. */
23#define CTASSERT(x) _Static_assert((x), #x)
24
25#else /* !(__STDC_VERSION__ >= 201112L) */
26
27/*
28 * If C11 is not available, expand __COUNTER__, or __INCLUDE_LEVEL__
29 * and __LINE__, or just __LINE__, with an intermediate preprocessor
30 * macro CTASSERT_EXPN, and then use CTASSERT_DECL to paste the
31 * expansions together into a unique name.
32 *
33 * We use this name as a typedef of an array type with a positive
34 * length if the assertion is true, and a negative length of the
35 * assertion is false, which is invalid and hence triggers a compiler
36 * error.
37 */
38#if defined(__COUNTER__)
39#define CTASSERT(x) CTASSERT_EXPN((x), c, __COUNTER__)
40#elif defined(__INCLUDE_LEVEL__)
41#define CTASSERT(x) CTASSERT_EXPN((x), __INCLUDE_LEVEL__, __LINE__)
42#else
43/* hope it's unique enough */
44#define CTASSERT(x) CTASSERT_EXPN((x), l, __LINE__)
45#endif /* defined(__COUNTER__) || ... */
46
47#define CTASSERT_EXPN(x, a, b) CTASSERT_DECL(x, a, b)
48#define CTASSERT_DECL(x, a, b) \
49 typedef char tor_ctassert_##a##_##b[(x) ? 1 : -1] ATTR_UNUSED; EAT_SEMICOLON
50
51#endif /* __STDC_VERSION__ >= 201112L */
52
53#endif /* !defined(TOR_CTASSERT_H) */
Utility macros to handle different features and behavior in different compilers.