#### Description:

This function creates a new YamlChan and optionally initialises its attributes.

A YamlChan is a specialised form of Channel which supports YAML I/O operations. Writing an Object to a YamlChan (using astWrite) will, if the Object is suitable, generate an YAML description of that Object, and reading from a YamlChan will create a new Object from its YAML description.

Normally, when you use a YamlChan, you should provide `"` source`"` and `"` sink`"` functions which connect it to an external data store by reading and writing the resulting text. These functions should perform any conversions needed between external character encodings and the internal ASCII encoding. If no such functions are supplied, a Channel will read from standard input and write to standard output.

Alternatively, a YamlChan can be told to read or write from specific text files using the SinkFile and SourceFile attributes, in which case no sink or source function need be supplied.

#### Synopsis

AstYamlChan ∗astYamlChan( const char ∗(∗ source)( void ), void (∗ sink)( const char ∗ ), const char ∗options, ... )

#### Parameters:

##### source

Pointer to a source function that takes no arguments and returns a pointer to a null-terminated string. If no value has been set for the SourceFile attribute, this function will be used by the YamlChan to obtain lines of input text. On each invocation, it should return a pointer to the next input line read from some external data store, and a NULL pointer when there are no more lines to read.

If `"` source`"` is NULL and no value has been set for the SourceFile attribute, the YamlChan will read from standard input instead.

##### sink

Pointer to a sink function that takes a pointer to a null-terminated string as an argument and returns void. If no value has been set for the SinkFile attribute, this function will be used by the YamlChan to deliver lines of output text. On each invocation, it should deliver the contents of the string supplied to some external data store.

If `"` sink`"` is NULL, and no value has been set for the SinkFile attribute, the YamlChan will write to standard output instead.

##### options

Pointer to a null-terminated string containing an optional comma-separated list of attribute assignments to be used for initialising the new YamlChan. The syntax used is identical to that for the astSet function and may include `"` printf`"` format specifiers identified by `"` %`"` symbols in the normal way.

##### ...

If the `"` options`"` string contains `"` %`"` format specifiers, then an optional list of additional arguments may follow it in order to supply values to be substituted for these specifiers. The rules for supplying these are identical to those for the astSet function (and for the C `"` printf`"` function).

#### Returned Value

##### astYamlChan()

A pointer to the new YamlChan.

#### Notes:

- If the external data source or sink uses a character encoding other than ASCII, the supplied source and sink functions should translate between the external character encoding and the internal ASCII encoding used by AST.

- A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.

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