[#fmt-system_error]
= xref:fmt.adoc[fmt]::system_error
:relfileprefix: ../
:mrdocs:

Constructs `std::system_error` with a message formatted with `fmt::format(fmt, args...)`. `error_code` is a system error code as given by `errno`.

== Synopsis

Declared in `<fmt/format.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename... T>
std::system_error
system_error(
    int error_code,
    xref:fmt/format_string.adoc[format_string<T...>] fmt,
    T&&... args);
----

== Description

*Example*:

// This throws std::system_error with the description // cannot open file 'madeup': No such file or directory // or similar (system message may vary). const char* filename = "madeup"; FILE* file = fopen(filename, "r"); if (!file) throw fmt::system_error(errno, "cannot open file '{}'", filename);

== Return Value

An exception type that includes an `error_code` value.


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