| // |
| // Copyright 2017 The Abseil Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| |
| #ifndef ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |
| #define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |
| |
| #include <string> |
| #include <utility> |
| |
| #include "absl/base/port.h" |
| #include "absl/meta/type_traits.h" // for void_t |
| |
| namespace absl { |
| namespace strings_internal { |
| |
| // Is a subclass of true_type or false_type, depending on whether or not |
| // T has a resize_uninitialized member. |
| template <typename T, typename = void> |
| struct HasResizeUninitialized : std::false_type {}; |
| template <typename T> |
| struct HasResizeUninitialized< |
| T, absl::void_t<decltype(std::declval<T>().resize_uninitialized(237))>> |
| : std::true_type {}; |
| |
| template <typename string_type> |
| void ResizeUninit(string_type* s, size_t new_size, std::true_type) { |
| s->resize_uninitialized(new_size); |
| } |
| template <typename string_type> |
| void ResizeUninit(string_type* s, size_t new_size, std::false_type) { |
| s->resize(new_size); |
| } |
| |
| // Returns true if the std::string implementation supports a resize where |
| // the new characters added to the std::string are left untouched. |
| // |
| // (A better name might be "STLStringSupportsUninitializedResize", alluding to |
| // the previous function.) |
| template <typename string_type> |
| inline constexpr bool STLStringSupportsNontrashingResize(string_type*) { |
| return HasResizeUninitialized<string_type>(); |
| } |
| |
| // Like str->resize(new_size), except any new characters added to "*str" as a |
| // result of resizing may be left uninitialized, rather than being filled with |
| // '0' bytes. Typically used when code is then going to overwrite the backing |
| // store of the std::string with known data. Uses a Google extension to std::string. |
| template <typename string_type, typename = void> |
| inline void STLStringResizeUninitialized(string_type* s, size_t new_size) { |
| ResizeUninit(s, new_size, HasResizeUninitialized<string_type>()); |
| } |
| |
| } // namespace strings_internal |
| } // namespace absl |
| |
| #endif // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |