[#BloombergLP-bdls-FilesystemUtil_CStringUtil]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdls.adoc[bdls]::FilesystemUtil_CStringUtil
:relfileprefix: ../../
:mrdocs:

This component‐private utility `struct` provides a namespace for the `flatten` overload set intended to be used in concert with an overload set consisting of a function template with a deduced argument and an non‐template overload accepting a `const char *`. The actual implementation of the functionality would be in the `const char *` overload whereas the purpose of the function template is to invoke the `const char *` overload with a null‐terminated string.

== Synopsis

Declared in `<bdls_filesystemutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
struct FilesystemUtil_CStringUtil;
----

== Description

The function template achieves null‐termination by recursively calling the function and supplying it with the result of `flatten` invoked on the deduced argument. This `flatten` invocation will call `c_str()` on various supported `string` types, will produce a temporary `bsl::string` for possibly non‐null‐terminated `bsl::string_view` or `bslstl::StringRef`, and will result in a `BSLMF_ASSERT` for any unsupported type. Calling the function with the temporary `bsl::string` produced from `bsl::string_view` or `bslstl::StringRef` will result in a second invocation of `flatten`, this time producing `const char *`, and finally calling the function with a null‐terminated string.

Note that the `bslstl::StringRef` overload for `flatten` is provided for backwards compatibility. Without it, the `bsl::string` and `std::string` overloads would be ambiguous. In new code, it is preferable to not provide `bslstl::StringRef` overload in a similar facility and require the clients to explicitly state the string type in their code, making a potential allocation obvious. The same considerations apply to `bsl::string_view`.

== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdls/FilesystemUtil_CStringUtil/flatten-00.adoc[`flatten`] 
| `flatten` overloads
|===



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