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

Stream buffer associated with an opened file descriptor.

== Synopsis

Declared in `<bdls_fdstreambuf.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class FdStreamBuf
    : public std::streambuf
----

== Description

This class, derived from the C++ standard library class `bsl::streambuf`, is a mechanism that can be associated with an opened file descriptor, and, except for changing the locale, enables the caller to invoke all the standard `bsl::streambuf` operations on that file descriptor. Note that objects of this class are always in exactly one of the 5 modes outlined in the enum `FdStreamBuf::FdStreamBufMode`.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `std::streambuf`
| 
|===

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdls/FdStreamBuf/2constructor.adoc[`FdStreamBuf`]         [.small]#[constructor]#
| Create a stream buffer associated with the specified file descriptor.
| xref:BloombergLP/bdls/FdStreamBuf/2destructor.adoc[`~FdStreamBuf`] [.small]#[destructor]# [.small]#[virtual]#
| Destroy this object and, if `willCloseOnReset` is `true`, close the file descriptor associated with this object, if any.
| xref:BloombergLP/bdls/FdStreamBuf/clear.adoc[`clear`] 
| Release any file descriptor associated with this stream buffer.
| xref:BloombergLP/bdls/FdStreamBuf/fileDescriptor.adoc[`fileDescriptor`] 
| Return the file descriptor associated with this object, or `FilesystemUtil::k_INVALID_FD` if this object is not currently associated with a file descriptor.
| xref:BloombergLP/bdls/FdStreamBuf/isOpened.adoc[`isOpened`] 
| Return `true` if this object is currently associated with a file descriptor, and `false` otherwise.
| xref:BloombergLP/bdls/FdStreamBuf/release.adoc[`release`] 
| Disassociate this stream buffer from its file descriptor without closing it.
| xref:BloombergLP/bdls/FdStreamBuf/reset.adoc[`reset`] 
| Associate this object with the specified file descriptor.
| xref:BloombergLP/bdls/FdStreamBuf/willCloseOnReset.adoc[`willCloseOnReset`] 
| Return `true` if this object will close the associated file descriptor the next time it is reset, cleared, or destroyed, and `false` otherwise.
|===


== Protected Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdls/FdStreamBuf/imbue.adoc[`imbue`]  [.small]#[virtual]#
| Set the locale for this object. This method has no effect. The behavior is undefined unless the specified `locale` is the same as `bsl::locale()`.
| xref:BloombergLP/bdls/FdStreamBuf/overflow.adoc[`overflow`]  [.small]#[virtual]#
| Flush the output buffer, optionally appending character `c` first.
| xref:BloombergLP/bdls/FdStreamBuf/pbackfail.adoc[`pbackfail`]  [.small]#[virtual]#
| Put back a character into the input sequence.
| xref:BloombergLP/bdls/FdStreamBuf/seekoff.adoc[`seekoff`]  [.small]#[virtual]#
| Set the file pointer associated with the file descriptor according to the specified `offset` and `whence`:
| xref:BloombergLP/bdls/FdStreamBuf/seekpos.adoc[`seekpos`]  [.small]#[virtual]#
| Seek to `offset` bytes from the beginning of the file.
| xref:BloombergLP/bdls/FdStreamBuf/setbuf.adoc[`setbuf`]  [.small]#[virtual]#
| Use `buffer` of capacity `numBytes` as this object's I/O buffer.
| xref:BloombergLP/bdls/FdStreamBuf/showmanyc.adoc[`showmanyc`]  [.small]#[virtual]#
| Return the number of characters remaining to be read.
| xref:BloombergLP/bdls/FdStreamBuf/sync.adoc[`sync`]  [.small]#[virtual]#
| If in output mode, flush the buffer to the associated file descriptor; otherwise do nothing. Return 0 on success, ‐1 otherwise.
| xref:BloombergLP/bdls/FdStreamBuf/underflow.adoc[`underflow`]  [.small]#[virtual]#
| Replenish the input buffer and return the next character of input.
| xref:BloombergLP/bdls/FdStreamBuf/xsgetn.adoc[`xsgetn`]  [.small]#[virtual]#
| Read up to `numBytes` characters into `buffer`.
| xref:BloombergLP/bdls/FdStreamBuf/xsputn.adoc[`xsputn`]  [.small]#[virtual]#
| Write up to `numBytes` characters from `buffer`.
|===



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