.. _syntax:

********************
Format String Syntax
********************

Formatting functions such as :ref:`fmt::format() <format>` and
:ref:`fmt::print() <print>` use the same format string syntax described in this
section.

Format strings contain "replacement fields" surrounded by curly braces ``{}``.
Anything that is not contained in braces is considered literal text, which is
copied unchanged to the output.  If you need to include a brace character in the
literal text, it can be escaped by doubling: ``{{`` and ``}}``.

The grammar for a replacement field is as follows:

.. productionlist:: sf
   replacement_field: "{" [`arg_id`] [":" (`format_spec` | `chrono_format_spec`)] "}"
   arg_id: `integer` | `identifier`                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            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