nullguard.h (2846B)
1 // Copyright 2022 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // ----------------------------------------------------------------------------- 16 // File: log/internal/nullguard.h 17 // ----------------------------------------------------------------------------- 18 // 19 // NullGuard exists such that NullGuard<T>::Guard(v) returns v, unless passed a 20 // nullptr_t, or a null char* or const char*, in which case it returns "(null)". 21 // This allows streaming NullGuard<T>::Guard(v) to an output stream without 22 // hitting undefined behavior for null values. 23 24 #ifndef ABSL_LOG_INTERNAL_NULLGUARD_H_ 25 #define ABSL_LOG_INTERNAL_NULLGUARD_H_ 26 27 #include <array> 28 #include <cstddef> 29 30 #include "absl/base/attributes.h" 31 #include "absl/base/config.h" 32 33 namespace absl { 34 ABSL_NAMESPACE_BEGIN 35 namespace log_internal { 36 37 ABSL_CONST_INIT ABSL_DLL extern const std::array<char, 7> kCharNull; 38 ABSL_CONST_INIT ABSL_DLL extern const std::array<signed char, 7> 39 kSignedCharNull; 40 ABSL_CONST_INIT ABSL_DLL extern const std::array<unsigned char, 7> 41 kUnsignedCharNull; 42 43 template <typename T> 44 struct NullGuard final { 45 static const T& Guard(const T& v) { return v; } 46 }; 47 template <> 48 struct NullGuard<char*> final { 49 static const char* Guard(const char* v) { return v ? v : kCharNull.data(); } 50 }; 51 template <> 52 struct NullGuard<const char*> final { 53 static const char* Guard(const char* v) { return v ? v : kCharNull.data(); } 54 }; 55 template <> 56 struct NullGuard<signed char*> final { 57 static const signed char* Guard(const signed char* v) { 58 return v ? v : kSignedCharNull.data(); 59 } 60 }; 61 template <> 62 struct NullGuard<const signed char*> final { 63 static const signed char* Guard(const signed char* v) { 64 return v ? v : kSignedCharNull.data(); 65 } 66 }; 67 template <> 68 struct NullGuard<unsigned char*> final { 69 static const unsigned char* Guard(const unsigned char* v) { 70 return v ? v : kUnsignedCharNull.data(); 71 } 72 }; 73 template <> 74 struct NullGuard<const unsigned char*> final { 75 static const unsigned char* Guard(const unsigned char* v) { 76 return v ? v : kUnsignedCharNull.data(); 77 } 78 }; 79 template <> 80 struct NullGuard<std::nullptr_t> final { 81 static const char* Guard(const std::nullptr_t&) { return kCharNull.data(); } 82 }; 83 84 } // namespace log_internal 85 ABSL_NAMESPACE_END 86 } // namespace absl 87 88 #endif // ABSL_LOG_INTERNAL_NULLGUARD_H_