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Diffstat (limited to 'absl/strings/str_cat.h')
| -rw-r--r-- | absl/strings/str_cat.h | 348 |
1 files changed, 348 insertions, 0 deletions
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h new file mode 100644 index 000000000000..5b4c9baacf59 --- /dev/null +++ b/absl/strings/str_cat.h @@ -0,0 +1,348 @@ +// +// 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. +// +// ----------------------------------------------------------------------------- +// File: str_cat.h +// ----------------------------------------------------------------------------- +// +// This package contains functions for efficiently concatenating and appending +// strings: `StrCat()` and `StrAppend()`. Most of the work within these routines +// is actually handled through use of a special AlphaNum type, which was +// designed to be used as a parameter type that efficiently manages conversion +// to strings and avoids copies in the above operations. +// +// Any routine accepting either a std::string or a number may accept `AlphaNum`. +// The basic idea is that by accepting a `const AlphaNum &` as an argument +// to your function, your callers will automagically convert bools, integers, +// and floating point values to strings for you. +// +// NOTE: Use of `AlphaNum` outside of the //absl/strings package is unsupported +// except for the specific case of function parameters of type `AlphaNum` or +// `const AlphaNum &`. In particular, instantiating `AlphaNum` directly as a +// stack variable is not supported. +// +// Conversion from 8-bit values is not accepted because, if it were, then an +// attempt to pass ':' instead of ":" might result in a 58 ending up in your +// result. +// +// Bools convert to "0" or "1". +// +// Floating point numbers are formatted with six-digit precision, which is +// the default for "std::cout <<" or printf "%g" (the same as "%.6g"). +// +// +// You can convert to hexadecimal output rather than decimal output using the +// `Hex` type contained here. To do so, pass `Hex(my_int)` as a parameter to +// `StrCat()` or `StrAppend()`. You may specify a minimum hex field width using +// a `PadSpec` enum, so the equivalent of `StringPrintf("%04x", my_int)` is +// `absl::StrCat(absl::Hex(my_int, absl::kZeroPad4))`. +// +// ----------------------------------------------------------------------------- + +#ifndef ABSL_STRINGS_STR_CAT_H_ +#define ABSL_STRINGS_STR_CAT_H_ + +#include <array> +#include <cstdint> +#include <string> +#include <type_traits> + +#include "absl/base/port.h" +#include "absl/strings/numbers.h" +#include "absl/strings/string_view.h" + +namespace absl { + +namespace strings_internal { +// AlphaNumBuffer allows a way to pass a std::string to StrCat without having to do +// memory allocation. It is simply a pair of a fixed-size character array, and +// a size. Please don't use outside of absl, yet. +template <size_t max_size> +struct AlphaNumBuffer { + std::array<char, max_size> data; + size_t size; +}; + +} // namespace strings_internal + +// Enum that specifies the number of significant digits to return in a `Hex` +// conversion and fill character to use. A `kZeroPad2` value, for example, would +// produce hexadecimal strings such as "0A","0F" and 'kSpacePad5' value would +// produce hexadecimal strings such as " A"," F". +enum PadSpec { + kNoPad = 1, + kZeroPad2, + kZeroPad3, + kZeroPad4, + kZeroPad5, + kZeroPad6, + kZeroPad7, + kZeroPad8, + kZeroPad9, + kZeroPad10, + kZeroPad11, + kZeroPad12, + kZeroPad13, + kZeroPad14, + kZeroPad15, + kZeroPad16, + + kSpacePad2 = kZeroPad2 + 64, + kSpacePad3, + kSpacePad4, + kSpacePad5, + kSpacePad6, + kSpacePad7, + kSpacePad8, + kSpacePad9, + kSpacePad10, + kSpacePad11, + kSpacePad12, + kSpacePad13, + kSpacePad14, + kSpacePad15, + kSpacePad16, +}; + +// ----------------------------------------------------------------------------- +// Hex +// ----------------------------------------------------------------------------- +// +// `Hex` stores a set of hexadecimal std::string conversion parameters for use +// within `AlphaNum` std::string conversions. +struct Hex { + uint64_t value; + uint8_t width; + char fill; + + template <typename Int> + explicit Hex(Int v, PadSpec spec = absl::kNoPad, + typename std::enable_if<sizeof(Int) == 1>::type* = nullptr) + : Hex(spec, static_cast<uint8_t>(v)) {} + template <typename Int> + explicit Hex(Int v, PadSpec spec = absl::kNoPad, + typename std::enable_if<sizeof(Int) == 2>::type* = nullptr) + : Hex(spec, static_cast<uint16_t>(v)) {} + template <typename Int> + explicit Hex(Int v, PadSpec spec = absl::kNoPad, + typename std::enable_if<sizeof(Int) == 4>::type* = nullptr) + : Hex(spec, static_cast<uint32_t>(v)) {} + template <typename Int> + explicit Hex(Int v, PadSpec spec = absl::kNoPad, + typename std::enable_if<sizeof(Int) == 8>::type* = nullptr) + : Hex(spec, static_cast<uint64_t>(v)) {} + + private: + Hex(PadSpec spec, uint64_t v) + : value(v), + width(spec == absl::kNoPad + ? 1 + : spec >= absl::kSpacePad2 ? spec - absl::kSpacePad2 + 2 + : spec - absl::kZeroPad2 + 2), + fill(spec >= absl::kSpacePad2 ? ' ' : '0') {} +}; + +// ----------------------------------------------------------------------------- +// AlphaNum +// ----------------------------------------------------------------------------- +// +// The `AlphaNum` class acts as the main parameter type for `StrCat()` and +// `StrAppend()`, providing efficient conversion of numeric, boolean, and +// hexadecimal values (through the `Hex` type) into strings. + +class AlphaNum { + public: + // No bool ctor -- bools convert to an integral type. + // A bool ctor would also convert incoming pointers (bletch). + + AlphaNum(int x) // NOLINT(runtime/explicit) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + AlphaNum(unsigned int x) // NOLINT(runtime/explicit) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + AlphaNum(long x) // NOLINT(*) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + AlphaNum(unsigned long x) // NOLINT(*) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + AlphaNum(long long x) // NOLINT(*) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + AlphaNum(unsigned long long x) // NOLINT(*) + : piece_(digits_, + numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {} + + AlphaNum(float f) // NOLINT(runtime/explicit) + : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {} + AlphaNum(double f) // NOLINT(runtime/explicit) + : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {} + + AlphaNum(Hex hex); // NOLINT(runtime/explicit) + + template <size_t size> + AlphaNum( // NOLINT(runtime/explicit) + const strings_internal::AlphaNumBuffer<size>& buf) + : piece_(&buf.data[0], buf.size) {} + + AlphaNum(const char* c_str) : piece_(c_str) {} // NOLINT(runtime/explicit) + AlphaNum(absl::string_view pc) : piece_(pc) {} // NOLINT(runtime/explicit) + template <typename Allocator> + AlphaNum( // NOLINT(runtime/explicit) + const std::basic_string<char, std::char_traits<char>, Allocator>& str) + : piece_(str) {} + + // Use std::string literals ":" instead of character literals ':'. + AlphaNum(char c) = delete; // NOLINT(runtime/explicit) + + AlphaNum(const AlphaNum&) = delete; + AlphaNum& operator=(const AlphaNum&) = delete; + + absl::string_view::size_type size() const { return piece_.size(); } + const char* data() const { return piece_.data(); } + absl::string_view Piece() const { return piece_; } + + // Normal enums are already handled by the integer formatters. + // This overload matches only scoped enums. + template <typename T, + typename = typename std::enable_if< + std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type> + AlphaNum(T e) // NOLINT(runtime/explicit) + : AlphaNum(static_cast<typename std::underlying_type<T>::type>(e)) {} + + private: + absl::string_view piece_; + char digits_[numbers_internal::kFastToBufferSize]; +}; + +// ----------------------------------------------------------------------------- +// StrCat() +// ----------------------------------------------------------------------------- +// +// Merges given strings or numbers, using no delimiter(s). +// +// `StrCat()` is designed to be the fastest possible way to construct a std::string +// out of a mix of raw C strings, string_views, strings, bool values, +// and numeric values. +// +// Don't use `StrCat()` for user-visible strings. The localization process +// works poorly on strings built up out of fragments. +// +// For clarity and performance, don't use `StrCat()` when appending to a +// std::string. Use `StrAppend()` instead. In particular, avoid using any of these +// (anti-)patterns: +// +// str.append(StrCat(...)) +// str += StrCat(...) +// str = StrCat(str, ...) +// +// The last case is the worst, with a potential to change a loop +// from a linear time operation with O(1) dynamic allocations into a +// quadratic time operation with O(n) dynamic allocations. +// +// See `StrAppend()` below for more information. + +namespace strings_internal { + +// Do not call directly - this is not part of the public API. +std::string CatPieces(std::initializer_list<absl::string_view> pieces); +void AppendPieces(std::string* dest, + std::initializer_list<absl::string_view> pieces); + +} // namespace strings_internal + +ABSL_MUST_USE_RESULT inline std::string StrCat() { return std::string(); } + +ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a) { + return std::string(a.data(), a.size()); +} + +ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b); +ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c); +ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c, const AlphaNum& d); + +// Support 5 or more arguments +template <typename... AV> +ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c, const AlphaNum& d, + const AlphaNum& e, + const AV&... args) { + return strings_internal::CatPieces( + {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(), + static_cast<const AlphaNum&>(args).Piece()...}); +} + +// ----------------------------------------------------------------------------- +// StrAppend() +// ----------------------------------------------------------------------------- +// +// Appends a std::string or set of strings to an existing std::string, in a similar +// fashion to `StrCat()`. +// +// WARNING: `StrAppend(&str, a, b, c, ...)` requires that none of the +// a, b, c, parameters be a reference into str. For speed, `StrAppend()` does +// not try to check each of its input arguments to be sure that they are not +// a subset of the std::string being appended to. That is, while this will work: +// +// std::string s = "foo"; +// s += s; +// +// This output is undefined: +// +// std::string s = "foo"; +// StrAppend(&s, s); +// +// This output is undefined as well, since `absl::string_view` does not own its +// data: +// +// std::string s = "foobar"; +// absl::string_view p = s; +// StrAppend(&s, p); + +inline void StrAppend(std::string*) {} +void StrAppend(std::string* dest, const AlphaNum& a); +void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b); +void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c); +void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c, const AlphaNum& d); + +// Support 5 or more arguments +template <typename... AV> +inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b, + const AlphaNum& c, const AlphaNum& d, const AlphaNum& e, + const AV&... args) { + strings_internal::AppendPieces( + dest, {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(), + static_cast<const AlphaNum&>(args).Piece()...}); +} + +// Helper function for the future StrCat default floating-point format, %.6g +// This is fast. +inline strings_internal::AlphaNumBuffer< + numbers_internal::kSixDigitsToBufferSize> +SixDigits(double d) { + strings_internal::AlphaNumBuffer<numbers_internal::kSixDigitsToBufferSize> + result; + result.size = numbers_internal::SixDigitsToBuffer(d, &result.data[0]); + return result; +} + +} // namespace absl + +#endif // ABSL_STRINGS_STR_CAT_H_ |