andrew@webrtc.org | a7b57da | 2012-10-22 18:19:23 +0000 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. |
| 3 | * |
| 4 | * Use of this source code is governed by a BSD-style license |
| 5 | * that can be found in the LICENSE file in the root of the source |
| 6 | * tree. An additional intellectual property rights grant can be found |
| 7 | * in the file PATENTS. All contributing project authors may |
| 8 | * be found in the AUTHORS file in the root of the source tree. |
| 9 | */ |
| 10 | |
andrew@webrtc.org | 5cc0d0b | 2014-05-04 03:04:26 +0000 | [diff] [blame^] | 11 | // Borrowed from Chromium's src/base/macros.h. |
andrew@webrtc.org | 2ba95be | 2013-10-22 12:50:00 +0000 | [diff] [blame] | 12 | |
andrew@webrtc.org | a7b57da | 2012-10-22 18:19:23 +0000 | [diff] [blame] | 13 | #ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_ |
| 14 | #define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_ |
| 15 | |
andrew@webrtc.org | 2ba95be | 2013-10-22 12:50:00 +0000 | [diff] [blame] | 16 | // The COMPILE_ASSERT macro can be used to verify that a compile time |
| 17 | // expression is true. For example, you could use it to verify the |
| 18 | // size of a static array: |
| 19 | // |
| 20 | // COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES, |
| 21 | // content_type_names_incorrect_size); |
| 22 | // |
| 23 | // or to make sure a struct is smaller than a certain size: |
| 24 | // |
| 25 | // COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large); |
| 26 | // |
| 27 | // The second argument to the macro is the name of the variable. If |
| 28 | // the expression is false, most compilers will issue a warning/error |
| 29 | // containing the name of the variable. |
| 30 | |
andrew@webrtc.org | d6b231e | 2013-10-23 19:11:32 +0000 | [diff] [blame] | 31 | // TODO(ajm): Hack to avoid multiple definitions until the base/ of webrtc and |
| 32 | // libjingle are merged. |
| 33 | #if !defined(COMPILE_ASSERT) |
andrew@webrtc.org | 5cc0d0b | 2014-05-04 03:04:26 +0000 | [diff] [blame^] | 34 | #if __cplusplus >= 201103L |
| 35 | // Under C++11, just use static_assert. |
| 36 | #define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg) |
| 37 | |
| 38 | #else |
andrew@webrtc.org | 2ba95be | 2013-10-22 12:50:00 +0000 | [diff] [blame] | 39 | template <bool> |
| 40 | struct CompileAssert { |
| 41 | }; |
| 42 | |
andrew@webrtc.org | 2ba95be | 2013-10-22 12:50:00 +0000 | [diff] [blame] | 43 | #define COMPILE_ASSERT(expr, msg) \ |
andrew@webrtc.org | 5cc0d0b | 2014-05-04 03:04:26 +0000 | [diff] [blame^] | 44 | typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] ALLOW_UNUSED |
| 45 | |
| 46 | #endif // __cplusplus >= 201103L |
| 47 | #endif // !defined(COMPILE_ASSERT) |
andrew@webrtc.org | 2ba95be | 2013-10-22 12:50:00 +0000 | [diff] [blame] | 48 | |
| 49 | // Implementation details of COMPILE_ASSERT: |
| 50 | // |
| 51 | // - COMPILE_ASSERT works by defining an array type that has -1 |
| 52 | // elements (and thus is invalid) when the expression is false. |
| 53 | // |
| 54 | // - The simpler definition |
| 55 | // |
| 56 | // #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1] |
| 57 | // |
| 58 | // does not work, as gcc supports variable-length arrays whose sizes |
| 59 | // are determined at run-time (this is gcc's extension and not part |
| 60 | // of the C++ standard). As a result, gcc fails to reject the |
| 61 | // following code with the simple definition: |
| 62 | // |
| 63 | // int foo; |
| 64 | // COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is |
| 65 | // // not a compile-time constant. |
| 66 | // |
| 67 | // - By using the type CompileAssert<(bool(expr))>, we ensures that |
| 68 | // expr is a compile-time constant. (Template arguments must be |
| 69 | // determined at compile-time.) |
| 70 | // |
| 71 | // - The outer parentheses in CompileAssert<(bool(expr))> are necessary |
| 72 | // to work around a bug in gcc 3.4.4 and 4.0.1. If we had written |
| 73 | // |
| 74 | // CompileAssert<bool(expr)> |
| 75 | // |
| 76 | // instead, these compilers will refuse to compile |
| 77 | // |
| 78 | // COMPILE_ASSERT(5 > 0, some_message); |
| 79 | // |
| 80 | // (They seem to think the ">" in "5 > 0" marks the end of the |
| 81 | // template argument list.) |
| 82 | // |
| 83 | // - The array size is (bool(expr) ? 1 : -1), instead of simply |
| 84 | // |
| 85 | // ((expr) ? 1 : -1). |
| 86 | // |
| 87 | // This is to avoid running into a bug in MS VC 7.1, which |
| 88 | // causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1. |
andrew@webrtc.org | a7b57da | 2012-10-22 18:19:23 +0000 | [diff] [blame] | 89 | |
| 90 | #endif // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_ |