diff options
Diffstat (limited to 'absl/strings/str_format.h')
| -rw-r--r-- | absl/strings/str_format.h | 80 |
1 files changed, 71 insertions, 9 deletions
diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h index 4b05c70c..3536b70e 100644 --- a/absl/strings/str_format.h +++ b/absl/strings/str_format.h @@ -191,9 +191,9 @@ class FormatCountCapture { // absl::StrFormat(formatString, "TheVillage", 6); // // A format string generally follows the POSIX syntax as used within the POSIX -// `printf` specification. +// `printf` specification. (Exceptions are noted below.) // -// (See http://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html.) +// (See http://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html) // // In specific, the `FormatSpec` supports the following type specifiers: // * `c` for characters @@ -211,6 +211,10 @@ class FormatCountCapture { // * `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. +// * `v` for values using the default format for a deduced type. These deduced +// types include many of the primitive types denoted here as well as +// user-defined types containing the proper extensions. (See below for more +// information.) // // Implementation-defined behavior: // * A null pointer provided to "%s" or "%p" is output as "(nil)". @@ -239,6 +243,15 @@ class FormatCountCapture { // "%s%d%n", "hello", 123, absl::FormatCountCapture(&n)); // EXPECT_EQ(8, n); // +// NOTE: the `v` specifier (for "value") is a type specifier not present in the +// POSIX specification. %v will format values according to their deduced type. +// `v` uses `d` for signed integer values, `u` for unsigned integer values, `g` +// for floating point values, and formats boolean values as "true"/"false" +// (instead of 1 or 0 for booleans formatted using d). `const char*` is not +// supported; please use `std:string` and `string_view`. `char` is also not +// supported due to ambiguity of the type. This specifier does not support +// modifiers. +// // The `FormatSpec` intrinsically supports all of these fundamental C++ types: // // * Characters: `char`, `signed char`, `unsigned char` @@ -570,6 +583,41 @@ ABSL_MUST_USE_RESULT inline bool FormatUntyped( // StrFormat Extensions //------------------------------------------------------------------------------ // +// AbslStringify() +// +// A simpler customization API for formatting user-defined types using +// absl::StrFormat(). The API relies on detecting an overload in the +// user-defined type's namespace of a free (non-member) `AbslStringify()` +// function as a friend definition with the following signature: +// +// template <typename Sink> +// void AbslStringify(Sink& sink, const X& value); +// +// An `AbslStringify()` overload for a type should only be declared in the same +// file and namespace as said type. +// +// Note that unlike with AbslFormatConvert(), AbslStringify() does not allow +// customization of allowed conversion characters. AbslStringify() uses `%v` as +// the underlying conversion specififer. Additionally, AbslStringify() supports +// use with absl::StrCat while AbslFormatConvert() does not. +// +// Example: +// +// struct Point { +// // To add formatting support to `Point`, we simply need to add a free +// // (non-member) function `AbslStringify()`. This method prints in the +// // request format using the underlying `%v` specifier. You can add such a +// // free function using a friend declaration within the body of the class. +// // The sink parameter is a templated type to avoid requiring dependencies. +// template <typename Sink> +// friend void AbslStringify(Sink& sink, const Point& p) { +// absl::Format(&sink, "(%v, %v)", p.x, p.y); +// } +// +// int x; +// int y; +// }; +// // AbslFormatConvert() // // The StrFormat library provides a customization API for formatting @@ -616,9 +664,9 @@ ABSL_MUST_USE_RESULT inline bool FormatUntyped( // AbslFormatConvert(const Point& p, const absl::FormatConversionSpec& spec, // absl::FormatSink* s) { // if (spec.conversion_char() == absl::FormatConversionChar::s) { -// s->Append(absl::StrCat("x=", p.x, " y=", p.y)); +// absl::Format(s, "x=%vy=%v", p.x, p.y); // } else { -// s->Append(absl::StrCat(p.x, ",", p.y)); +// absl::Format(s, "%v,%v", p.x, p.y); // } // return {true}; // } @@ -637,7 +685,7 @@ enum class FormatConversionChar : uint8_t { c, s, // text d, i, o, u, x, X, // int f, F, e, E, g, G, a, A, // float - n, p // misc + n, p, v // misc }; // clang-format on @@ -757,6 +805,7 @@ enum class FormatConversionCharSet : uint64_t { // misc n = str_format_internal::FormatConversionCharToConvInt('n'), p = str_format_internal::FormatConversionCharToConvInt('p'), + v = str_format_internal::FormatConversionCharToConvInt('v'), // Used for width/precision '*' specification. kStar = static_cast<uint64_t>( @@ -771,23 +820,36 @@ enum class FormatConversionCharSet : uint64_t { // FormatSink // -// An abstraction to which conversions write their string data. +// A format sink is a generic abstraction to which conversions may write their +// formatted string data. `absl::FormatConvert()` uses this sink to write its +// formatted string. // class FormatSink { public: - // Appends `count` copies of `ch`. + // FormatSink::Append() + // + // Appends `count` copies of `ch` to the format sink. void Append(size_t count, char ch) { sink_->Append(count, ch); } + // Overload of FormatSink::Append() for appending the characters of a string + // view to a format sink. void Append(string_view v) { sink_->Append(v); } - // Appends the first `precision` bytes of `v`. If this is less than - // `width`, spaces will be appended first (if `left` is false), or + // FormatSink::PutPaddedString() + // + // Appends `precision` number of bytes of `v` to the format sink. If this is + // less than `width`, spaces will be appended first (if `left` is false), or // after (if `left` is true) to ensure the total amount appended is // at least `width`. bool PutPaddedString(string_view v, int width, int precision, bool left) { return sink_->PutPaddedString(v, width, precision, left); } + // Support `absl::Format(&sink, format, args...)`. + friend void AbslFormatFlush(FormatSink* sink, absl::string_view v) { + sink->Append(v); + } + private: friend str_format_internal::FormatSinkImpl; explicit FormatSink(str_format_internal::FormatSinkImpl* s) : sink_(s) {} |