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Diffstat (limited to 'absl/strings/str_format.h')
| -rw-r--r-- | absl/strings/str_format.h | 514 |
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diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h new file mode 100644 index 00000000..7b19d411 --- /dev/null +++ b/absl/strings/str_format.h @@ -0,0 +1,514 @@ +// +// Copyright 2018 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_format.h +// ----------------------------------------------------------------------------- +// +// The `str_format` library is a typesafe replacement for the family of +// `printf()` string formatting routines within the `<cstdio>` standard library +// header. Like the `printf` family, the `str_format` uses a "format string" to +// perform argument substitutions based on types. +// +// Example: +// +// string s = absl::StrFormat("%s %s You have $%d!", "Hello", name, dollars); +// +// The library consists of the following basic utilities: +// +// * `absl::StrFormat()`, a type-safe replacement for `std::sprintf()`, to +// write a format string to a `string` value. +// * `absl::StrAppendFormat()` to append a format string to a `string` +// * `absl::StreamFormat()` to more efficiently write a format string to a +// stream, such as`std::cout`. +// * `absl::PrintF()`, `absl::FPrintF()` and `absl::SNPrintF()` as +// replacements for `std::printf()`, `std::fprintf()` and `std::snprintf()`. +// +// Note: a version of `std::sprintf()` is not supported as it is +// generally unsafe due to buffer overflows. +// +// Additionally, you can provide a format string (and its associated arguments) +// using one of the following abstractions: +// +// * A `FormatSpec` class template fully encapsulates a format string and its +// type arguments and is usually provided to `str_format` functions as a +// variadic argument of type `FormatSpec<Arg...>`. The `FormatSpec<Args...>` +// template is evaluated at compile-time, providing type safety. +// * A `ParsedFormat` instance, which encapsulates a specific, pre-compiled +// format string for a specific set of type(s), and which can be passed +// between API boundaries. (The `FormatSpec` type should not be used +// directly.) +// +// The `str_format` library provides the ability to output its format strings to +// arbitrary sink types: +// +// * A generic `Format()` function to write outputs to arbitrary sink types, +// which must implement a `RawSinkFormat` interface. (See +// `str_format_sink.h` for more information.) +// +// * A `FormatUntyped()` function that is similar to `Format()` except it is +// loosely typed. `FormatUntyped()` is not a template and does not perform +// any compile-time checking of the format string; instead, it returns a +// boolean from a runtime check. +// +// In addition, the `str_format` library provides extension points for +// augmenting formatting to new types. These extensions are fully documented +// within the `str_format_extension.h` header file. +#ifndef ABSL_STRINGS_STR_FORMAT_H_ +#define ABSL_STRINGS_STR_FORMAT_H_ + +#include <cstdio> +#include <string> + +#include "absl/strings/internal/str_format/arg.h" // IWYU pragma: export +#include "absl/strings/internal/str_format/bind.h" // IWYU pragma: export +#include "absl/strings/internal/str_format/checker.h" // IWYU pragma: export +#include "absl/strings/internal/str_format/extension.h" // IWYU pragma: export +#include "absl/strings/internal/str_format/parser.h" // IWYU pragma: export + +namespace absl { +inline namespace lts_2018_12_18 { + +// UntypedFormatSpec +// +// A type-erased class that can be used directly within untyped API entry +// points. An `UntypedFormatSpec` is specifically used as an argument to +// `FormatUntyped()`. +// +// Example: +// +// absl::UntypedFormatSpec format("%d"); +// string out; +// CHECK(absl::FormatUntyped(&out, format, {absl::FormatArg(1)})); +class UntypedFormatSpec { + public: + UntypedFormatSpec() = delete; + UntypedFormatSpec(const UntypedFormatSpec&) = delete; + UntypedFormatSpec& operator=(const UntypedFormatSpec&) = delete; + + explicit UntypedFormatSpec(string_view s) : spec_(s) {} + + protected: + explicit UntypedFormatSpec(const str_format_internal::ParsedFormatBase* pc) + : spec_(pc) {} + + private: + friend str_format_internal::UntypedFormatSpecImpl; + str_format_internal::UntypedFormatSpecImpl spec_; +}; + +// FormatStreamed() +// +// Takes a streamable argument and returns an object that can print it +// with '%s'. Allows printing of types that have an `operator<<` but no +// intrinsic type support within `StrFormat()` itself. +// +// Example: +// +// absl::StrFormat("%s", absl::FormatStreamed(obj)); +template <typename T> +str_format_internal::StreamedWrapper<T> FormatStreamed(const T& v) { + return str_format_internal::StreamedWrapper<T>(v); +} + +// FormatCountCapture +// +// This class provides a way to safely wrap `StrFormat()` captures of `%n` +// conversions, which denote the number of characters written by a formatting +// operation to this point, into an integer value. +// +// This wrapper is designed to allow safe usage of `%n` within `StrFormat(); in +// the `printf()` family of functions, `%n` is not safe to use, as the `int *` +// buffer can be used to capture arbitrary data. +// +// Example: +// +// int n = 0; +// string s = absl::StrFormat("%s%d%n", "hello", 123, +// absl::FormatCountCapture(&n)); +// EXPECT_EQ(8, n); +class FormatCountCapture { + public: + explicit FormatCountCapture(int* p) : p_(p) {} + + private: + // FormatCountCaptureHelper is used to define FormatConvertImpl() for this + // class. + friend struct str_format_internal::FormatCountCaptureHelper; + // Unused() is here because of the false positive from -Wunused-private-field + // p_ is used in the templated function of the friend FormatCountCaptureHelper + // class. + int* Unused() { return p_; } + int* p_; +}; + +// FormatSpec +// +// The `FormatSpec` type defines the makeup of a format string within the +// `str_format` library. You should not need to use or manipulate this type +// directly. A `FormatSpec` is a variadic class template that is evaluated at +// compile-time, according to the format string and arguments that are passed +// to it. +// +// For a `FormatSpec` to be valid at compile-time, it must be provided as +// either: +// +// * A `constexpr` literal or `absl::string_view`, which is how it most often +// used. +// * A `ParsedFormat` instantiation, which ensures the format string is +// valid before use. (See below.) +// +// Example: +// +// // Provided as a string literal. +// absl::StrFormat("Welcome to %s, Number %d!", "The Village", 6); +// +// // Provided as a constexpr absl::string_view. +// constexpr absl::string_view formatString = "Welcome to %s, Number %d!"; +// absl::StrFormat(formatString, "The Village", 6); +// +// // Provided as a pre-compiled ParsedFormat object. +// // Note that this example is useful only for illustration purposes. +// absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!"); +// absl::StrFormat(formatString, "TheVillage", 6); +// +// A format string generally follows the POSIX syntax as used within the POSIX +// `printf` specification. +// +// (See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/printf.html.) +// +// In specific, the `FormatSpec` supports the following type specifiers: +// * `c` for characters +// * `s` for strings +// * `d` or `i` for integers +// * `o` for unsigned integer conversions into octal +// * `x` or `X` for unsigned integer conversions into hex +// * `u` for unsigned integers +// * `f` or `F` for floating point values into decimal notation +// * `e` or `E` for floating point values into exponential notation +// * `a` or `A` for floating point values into hex exponential notation +// * `g` or `G` for floating point values into decimal or exponential +// notation based on their precision +// * `p` for pointer address values +// * `n` for the special case of writing out the number of characters +// written to this point. The resulting value must be captured within an +// `absl::FormatCountCapture` type. +// +// NOTE: `o`, `x\X` and `u` will convert signed values to their unsigned +// counterpart before formatting. +// +// Examples: +// "%c", 'a' -> "a" +// "%c", 32 -> " " +// "%s", "C" -> "C" +// "%s", std::string("C++") -> "C++" +// "%d", -10 -> "-10" +// "%o", 10 -> "12" +// "%x", 16 -> "10" +// "%f", 123456789 -> "123456789.000000" +// "%e", .01 -> "1.00000e-2" +// "%a", -3.0 -> "-0x1.8p+1" +// "%g", .01 -> "1e-2" +// "%p", *int -> "0x7ffdeb6ad2a4" +// +// int n = 0; +// string s = absl::StrFormat( +// "%s%d%n", "hello", 123, absl::FormatCountCapture(&n)); +// EXPECT_EQ(8, n); +// +// The `FormatSpec` intrinsically supports all of these fundamental C++ types: +// +// * Characters: `char`, `signed char`, `unsigned char` +// * Integers: `int`, `short`, `unsigned short`, `unsigned`, `long`, +// `unsigned long`, `long long`, `unsigned long long` +// * Floating-point: `float`, `double`, `long double` +// +// However, in the `str_format` library, a format conversion specifies a broader +// C++ conceptual category instead of an exact type. For example, `%s` binds to +// any string-like argument, so `std::string`, `absl::string_view`, and +// `const char*` are all accepted. Likewise, `%d` accepts any integer-like +// argument, etc. + +template <typename... Args> +using FormatSpec = + typename str_format_internal::FormatSpecDeductionBarrier<Args...>::type; + +// ParsedFormat +// +// A `ParsedFormat` is a class template representing a preparsed `FormatSpec`, +// with template arguments specifying the conversion characters used within the +// format string. Such characters must be valid format type specifiers, and +// these type specifiers are checked at compile-time. +// +// Instances of `ParsedFormat` can be created, copied, and reused to speed up +// formatting loops. A `ParsedFormat` may either be constructed statically, or +// dynamically through its `New()` factory function, which only constructs a +// runtime object if the format is valid at that time. +// +// Example: +// +// // Verified at compile time. +// absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!"); +// absl::StrFormat(formatString, "TheVillage", 6); +// +// // Verified at runtime. +// auto format_runtime = absl::ParsedFormat<'d'>::New(format_string); +// if (format_runtime) { +// value = absl::StrFormat(*format_runtime, i); +// } else { +// ... error case ... +// } +template <char... Conv> +using ParsedFormat = str_format_internal::ExtendedParsedFormat< + str_format_internal::ConversionCharToConv(Conv)...>; + +// StrFormat() +// +// Returns a `string` given a `printf()`-style format string and zero or more +// additional arguments. Use it as you would `sprintf()`. `StrFormat()` is the +// primary formatting function within the `str_format` library, and should be +// used in most cases where you need type-safe conversion of types into +// formatted strings. +// +// The format string generally consists of ordinary character data along with +// one or more format conversion specifiers (denoted by the `%` character). +// Ordinary character data is returned unchanged into the result string, while +// each conversion specification performs a type substitution from +// `StrFormat()`'s other arguments. See the comments for `FormatSpec` for full +// information on the makeup of this format string. +// +// Example: +// +// string s = absl::StrFormat( +// "Welcome to %s, Number %d!", "The Village", 6); +// EXPECT_EQ("Welcome to The Village, Number 6!", s); +// +// Returns an empty string in case of error. +template <typename... Args> +ABSL_MUST_USE_RESULT std::string StrFormat(const FormatSpec<Args...>& format, + const Args&... args) { + return str_format_internal::FormatPack( + str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// StrAppendFormat() +// +// Appends to a `dst` string given a format string, and zero or more additional +// arguments, returning `*dst` as a convenience for chaining purposes. Appends +// nothing in case of error (but possibly alters its capacity). +// +// Example: +// +// string orig("For example PI is approximately "); +// std::cout << StrAppendFormat(&orig, "%12.6f", 3.14); +template <typename... Args> +std::string& StrAppendFormat(std::string* dst, const FormatSpec<Args...>& format, + const Args&... args) { + return str_format_internal::AppendPack( + dst, str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// StreamFormat() +// +// Writes to an output stream given a format string and zero or more arguments, +// generally in a manner that is more efficient than streaming the result of +// `absl:: StrFormat()`. The returned object must be streamed before the full +// expression ends. +// +// Example: +// +// std::cout << StreamFormat("%12.6f", 3.14); +template <typename... Args> +ABSL_MUST_USE_RESULT str_format_internal::Streamable StreamFormat( + const FormatSpec<Args...>& format, const Args&... args) { + return str_format_internal::Streamable( + str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// PrintF() +// +// Writes to stdout given a format string and zero or more arguments. This +// function is functionally equivalent to `std::printf()` (and type-safe); +// prefer `absl::PrintF()` over `std::printf()`. +// +// Example: +// +// std::string_view s = "Ulaanbaatar"; +// absl::PrintF("The capital of Mongolia is %s", s); +// +// Outputs: "The capital of Mongolia is Ulaanbaatar" +// +template <typename... Args> +int PrintF(const FormatSpec<Args...>& format, const Args&... args) { + return str_format_internal::FprintF( + stdout, str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// FPrintF() +// +// Writes to a file given a format string and zero or more arguments. This +// function is functionally equivalent to `std::fprintf()` (and type-safe); +// prefer `absl::FPrintF()` over `std::fprintf()`. +// +// Example: +// +// std::string_view s = "Ulaanbaatar"; +// absl::FPrintF(stdout, "The capital of Mongolia is %s", s); +// +// Outputs: "The capital of Mongolia is Ulaanbaatar" +// +template <typename... Args> +int FPrintF(std::FILE* output, const FormatSpec<Args...>& format, + const Args&... args) { + return str_format_internal::FprintF( + output, str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// SNPrintF() +// +// Writes to a sized buffer given a format string and zero or more arguments. +// This function is functionally equivalent to `std::snprintf()` (and +// type-safe); prefer `absl::SNPrintF()` over `std::snprintf()`. +// +// Example: +// +// std::string_view s = "Ulaanbaatar"; +// char output[128]; +// absl::SNPrintF(output, sizeof(output), +// "The capital of Mongolia is %s", s); +// +// Post-condition: output == "The capital of Mongolia is Ulaanbaatar" +// +template <typename... Args> +int SNPrintF(char* output, std::size_t size, const FormatSpec<Args...>& format, + const Args&... args) { + return str_format_internal::SnprintF( + output, size, str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// ----------------------------------------------------------------------------- +// Custom Output Formatting Functions +// ----------------------------------------------------------------------------- + +// FormatRawSink +// +// FormatRawSink is a type erased wrapper around arbitrary sink objects +// specifically used as an argument to `Format()`. +// FormatRawSink does not own the passed sink object. The passed object must +// outlive the FormatRawSink. +class FormatRawSink { + public: + // Implicitly convert from any type that provides the hook function as + // described above. + template <typename T, + typename = typename std::enable_if<std::is_constructible< + str_format_internal::FormatRawSinkImpl, T*>::value>::type> + FormatRawSink(T* raw) // NOLINT + : sink_(raw) {} + + private: + friend str_format_internal::FormatRawSinkImpl; + str_format_internal::FormatRawSinkImpl sink_; +}; + +// Format() +// +// Writes a formatted string to an arbitrary sink object (implementing the +// `absl::FormatRawSink` interface), using a format string and zero or more +// additional arguments. +// +// By default, `string` and `std::ostream` are supported as destination objects. +// +// `absl::Format()` is a generic version of `absl::StrFormat(), for custom +// sinks. The format string, like format strings for `StrFormat()`, is checked +// at compile-time. +// +// On failure, this function returns `false` and the state of the sink is +// unspecified. +template <typename... Args> +bool Format(FormatRawSink raw_sink, const FormatSpec<Args...>& format, + const Args&... args) { + return str_format_internal::FormatUntyped( + str_format_internal::FormatRawSinkImpl::Extract(raw_sink), + str_format_internal::UntypedFormatSpecImpl::Extract(format), + {str_format_internal::FormatArgImpl(args)...}); +} + +// FormatArg +// +// A type-erased handle to a format argument specifically used as an argument to +// `FormatUntyped()`. You may construct `FormatArg` by passing +// reference-to-const of any printable type. `FormatArg` is both copyable and +// assignable. The source data must outlive the `FormatArg` instance. See +// example below. +// +using FormatArg = str_format_internal::FormatArgImpl; + +// FormatUntyped() +// +// Writes a formatted string to an arbitrary sink object (implementing the +// `absl::FormatRawSink` interface), using an `UntypedFormatSpec` and zero or +// more additional arguments. +// +// This function acts as the most generic formatting function in the +// `str_format` library. The caller provides a raw sink, an unchecked format +// string, and (usually) a runtime specified list of arguments; no compile-time +// checking of formatting is performed within this function. As a result, a +// caller should check the return value to verify that no error occurred. +// On failure, this function returns `false` and the state of the sink is +// unspecified. +// +// The arguments are provided in an `absl::Span<const absl::FormatArg>`. +// Each `absl::FormatArg` object binds to a single argument and keeps a +// reference to it. The values used to create the `FormatArg` objects must +// outlive this function call. (See `str_format_arg.h` for information on +// the `FormatArg` class.)_ +// +// Example: +// +// std::optional<string> FormatDynamic(const string& in_format, +// const vector<string>& in_args) { +// string out; +// std::vector<absl::FormatArg> args; +// for (const auto& v : in_args) { +// // It is important that 'v' is a reference to the objects in in_args. +// // The values we pass to FormatArg must outlive the call to +// // FormatUntyped. +// args.emplace_back(v); +// } +// absl::UntypedFormatSpec format(in_format); +// if (!absl::FormatUntyped(&out, format, args)) { +// return std::nullopt; +// } +// return std::move(out); +// } +// +ABSL_MUST_USE_RESULT inline bool FormatUntyped( + FormatRawSink raw_sink, const UntypedFormatSpec& format, + absl::Span<const FormatArg> args) { + return str_format_internal::FormatUntyped( + str_format_internal::FormatRawSinkImpl::Extract(raw_sink), + str_format_internal::UntypedFormatSpecImpl::Extract(format), args); +} + +} // inline namespace lts_2018_12_18 +} // namespace absl +#endif // ABSL_STRINGS_STR_FORMAT_H_ |