As can be seen from the table above, most of the specifiers remain the same
-which simplifies migration from printf. Notable difference is in
-the alignment specification. The proposed syntax allows left, center, and right
-alignment represented by '<', '^', and
-'>' respectively which is more expressive than the corresponding
-printf syntax. The latter only supports left and right (the default)
-alignment.
+which simplifies migration from printf. Notable difference is
+in the alignment specification. The proposed syntax allows left, center,
+and right alignment represented by '<', '^',
+and '>' respectively which is more expressive than the
+corresponding printf syntax. The latter only supports left and
+right (the default) alignment.
@@ -215,9 +216,9 @@ The same formatting cannot be easily achieved with printf.
-Both the format string syntax and the API are designed with extensibility in mind. -The mini-language can be extended for user-defined types and users can provide -functions that do parsing and formatting for such types. +Both the format string syntax and the API are designed with extensibility in +mind. The mini-language can be extended for user-defined types and users can +provide functions that do parsing and formatting for such types.
The general syntax of a replacement field in a format string is @@ -234,7 +235,7 @@ functions that do parsing and formatting for such types.
where format-spec is predefined for built-in types, but can be
customized for user-defined types. For example, the syntax can be extended
-for put_time-like date and time formatting:
+for put_time-like date and time formatting
@@ -242,16 +243,51 @@ for put_time-like date and time formatting:
std::string date = std::format("The date is {0:%Y-%m-%d}.", *std::localtime(&t));
-TODO: API
+by providing an overload of std::format_arg for
+std::tm:
<cstdarg>. The type information is captured
+automatically and passed to formatters guaranteeing type safety and making
+many of the printf specifiers redundant (see
+Format String Syntax). Buffer management is also automatic to prevent
+buffer overflow errors common to printf.
TODO
++As pointed out in + +P0067R1: Elementary string conversions there is a number of use +cases that do not require internationalization support, but do require high +throughput when produced by a server. These include various text-based +interchange formats such as JSON or XML. The need for locale-independent +functions for conversions between integers and strings and between +floating-point numbers and strings has also been highlighted in + +N4412: Shortcomings of iostreams. Therefore a user should be able to +easily control whether to use locales or not during formatting. +
+ +
+We follow Python's approach [3] and designate a separate format
+specifier 'n' for locale-aware numeric formatting. It applies to
+all integral and floating-point types. All other specifiers produce output
+unaffected by locale settings.
+
TODO
+TODO
+TODO
@@ -260,7 +296,7 @@ std::string date = std::format("The date is {0:%Y-%m-%d}.", *std::localtime(&t))The ideas proposed in this paper have been implemented in the open-source fmt -library. TODO: link +library. TODO: link and mention other implementations (Boost Format, FastFormat)