[#absl-FormatUntyped]
= xref:absl.adoc[absl]::FormatUntyped
:relfileprefix: ../
:mrdocs:

Writes a formatted string to an arbitrary sink object (implementing the `absl::FormatRawSink` interface), using an `UntypedFormatSpec` and zero or more additional arguments.

== Synopsis

Declared in `<absl/strings/str_format.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[nodiscard]]
bool
FormatUntyped(
    xref:absl/FormatRawSink.adoc[FormatRawSink] raw_sink,
    xref:absl/UntypedFormatSpec.adoc[UntypedFormatSpec] const& format,
    xref:absl/Span.adoc[absl::Span<FormatArg const>] args);
----

== Description

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.

Example:

std::optional<std::string> FormatDynamic( const std::string& in_format, const vector<std::string>& in_args) { std::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); }

== Return Value

`true` on success, `false` on error.

[NOTE]
====
The return value https://en.cppreference.com/cpp/language/attributes/nodiscard[should not be discarded^].
====
== Parameters

[cols="1,4"]
|===
| Name| Description
| *raw_sink*
| The sink that receives the formatted output.
| *format*
| The untyped format spec.
| *args*
| The arguments substituted into the format string.
|===


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