If you want to save the whole document to a file, you can use one of the following functions:

bool xml_document::save_file(const char* path, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto) const;
bool xml_document::save_file(const wchar_t* path, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto) const;

These functions accept file path as its first argument, and also three optional arguments, which specify indentation and other output options (see Output options) and output data encoding (see Encodings). The path has the target operating system format, so it can be a relative or absolute one, it should have the delimiters of the target system, it should have the exact case if the target file system is case-sensitive, etc.

File path is passed to the system file opening function as is in case of the first function (which accepts const char* path); the second function either uses a special file opening function if it is provided by the runtime library or converts the path to UTF-8 and uses the system file opening function.

save_file opens the target file for writing, outputs the requested header (by default a document declaration is output, unless the document already has one), and then saves the document contents. If the file could not be opened, the function returns false. Calling save_file is equivalent to creating an xml_writer_file object with FILE* handle as the only constructor argument and then calling save; see Saving document via writer interface for writer interface details.

This is a simple example of saving XML document to file (samples/save_file.cpp):

// save document to file
std::cout << "Saving result: " << doc.save_file("save_file_output.xml") << std::endl;

To enhance interoperability pugixml provides functions for saving document to any object which implements C++ std::ostream interface. This allows you to save documents to any standard C++ stream (i.e. file stream) or any third-party compliant implementation (i.e. Boost Iostreams). Most notably, this allows for easy debug output, since you can use std::cout stream as saving target. There are two functions, one works with narrow character streams, another handles wide character ones:

void xml_document::save(std::ostream& stream, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto) const;
void xml_document::save(std::wostream& stream, const char_t* indent = "\t", unsigned int flags = format_default) const;

save with std::ostream argument saves the document to the stream in the same way as save_file (i.e. with requested header and with encoding conversions). On the other hand, save with std::wstream argument saves the document to the wide stream with encoding_wchar encoding. Because of this, using save with wide character streams requires careful (usually platform-specific) stream setup (i.e. using the imbue function). Generally use of wide streams is discouraged, however it provides you with the ability to save documents to non-Unicode encodings, i.e. you can save Shift-JIS encoded data if you set the correct locale.

Calling save with stream target is equivalent to creating an xml_writer_stream object with stream as the only constructor argument and then calling save; see Saving document via writer interface for writer interface details.

This is a simple example of saving XML document to standard output (samples/save_stream.cpp):

// save document to standard output
std::cout << "Document:\n";
doc.save(std::cout);

All of the above saving functions are implemented in terms of writer interface. This is a simple interface with a single function, which is called several times during output process with chunks of document data as input:

class xml_writer
{
public:
    virtual void write(const void* data, size_t size) = 0;
};

void xml_document::save(xml_writer& writer, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto) const;

In order to output the document via some custom transport, for example sockets, you should create an object which implements xml_writer interface and pass it to save function. xml_writer::write function is called with a buffer as an input, where data points to buffer start, and size is equal to the buffer size in bytes. write implementation must write the buffer to the transport; it can not save the passed buffer pointer, as the buffer contents will change after write returns. The buffer contains the chunk of document data in the desired encoding.

write function is called with relatively large blocks (size is usually several kilobytes, except for the last block that may be small), so there is often no need for additional buffering in the implementation.

This is a simple example of custom writer for saving document data to STL string (samples/save_custom_writer.cpp); read the sample code for more complex examples:

struct xml_string_writer: pugi::xml_writer
{
    std::string result;

    virtual void write(const void* data, size_t size)
    {
        result += std::string(static_cast<const char*>(data), size);
    }
};

While the previously described functions save the whole document to the destination, it is easy to save a single subtree. The following functions are provided:

void xml_node::print(std::ostream& os, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto, unsigned int depth = 0) const;
void xml_node::print(std::wostream& os, const char_t* indent = "\t", unsigned int flags = format_default, unsigned int depth = 0) const;
void xml_node::print(xml_writer& writer, const char_t* indent = "\t", unsigned int flags = format_default, xml_encoding encoding = encoding_auto, unsigned int depth = 0) const;

These functions have the same arguments with the same meaning as the corresponding xml_document::save functions, and allow you to save the subtree to either a C++ IOstream or to any object that implements xml_writer interface.

Saving a subtree differs from saving the whole document: the process behaves as if format_write_bom is off, and format_no_declaration is on, even if actual values of the flags are different. This means that BOM is not written to the destination, and document declaration is only written if it is the node itself or is one of node's children. Note that this also holds if you're saving a document; this example (samples/save_subtree.cpp) illustrates the difference:

// get a test document
pugi::xml_document doc;
doc.load("<foo bar='baz'><call>hey</call></foo>");

// print document to standard output (prints <?xml version="1.0"?><foo bar="baz"><call>hey</call></foo>)
doc.save(std::cout, "", pugi::format_raw);
std::cout << std::endl;

// print document to standard output as a regular node (prints <foo bar="baz"><call>hey</call></foo>)
doc.print(std::cout, "", pugi::format_raw);
std::cout << std::endl;

// print a subtree to standard output (prints <call>hey</call>)
doc.child("foo").child("call").print(std::cout, "", pugi::format_raw);
std::cout << std::endl;

All saving functions accept the optional parameter flags. This is a bitmask that customizes the output format; you can select the way the document nodes are printed and select the needed additional information that is output before the document contents.

	Note
	You should use the usual bitwise arithmetics to manipulate the bitmask: to enable a flag, use mask | flag; to disable a flag, use mask & ~flag.

These flags control the resulting tree contents:

These flags control the additional output information:

Additionally, there is one predefined option mask:

This is an example that shows the outputs of different output options (samples/save_options.cpp):

// get a test document
pugi::xml_document doc;
doc.load("<foo bar='baz'><call>hey</call></foo>");

// default options; prints
// <?xml version="1.0"?>
// <foo bar="baz">
//         <call>hey</call>
// </foo>
doc.save(std::cout);
std::cout << std::endl;

// default options with custom indentation string; prints
// <?xml version="1.0"?>
// <foo bar="baz">
// --<call>hey</call>
// </foo>
doc.save(std::cout, "--");
std::cout << std::endl;

// default options without indentation; prints
// <?xml version="1.0"?>
// <foo bar="baz">
// <call>hey</call>
// </foo>
doc.save(std::cout, "\t", pugi::format_default & ~pugi::format_indent); // can also pass "" instead of indentation string for the same effect
std::cout << std::endl;

// raw output; prints
// <?xml version="1.0"?><foo bar="baz"><call>hey</call></foo>
doc.save(std::cout, "\t", pugi::format_raw);
std::cout << std::endl << std::endl;

// raw output without declaration; prints
// <foo bar="baz"><call>hey</call></foo>
doc.save(std::cout, "\t", pugi::format_raw | pugi::format_no_declaration);
std::cout << std::endl;

pugixml supports all popular Unicode encodings (UTF-8, UTF-16 (big and little endian), UTF-32 (big and little endian); UCS-2 is naturally supported since it's a strict subset of UTF-16) and handles all encoding conversions during output. The output encoding is set via the encoding parameter of saving functions, which is of type xml_encoding. The possible values for the encoding are documented in Encodings; the only flag that has a different meaning is encoding_auto.

While all other flags set the exact encoding, encoding_auto is meant for automatic encoding detection. The automatic detection does not make sense for output encoding, since there is usually nothing to infer the actual encoding from, so here encoding_auto means UTF-8 encoding, which is the most popular encoding for XML data storage. This is also the default value of output encoding; specify another value if you do not want UTF-8 encoded output.

Also note that wide stream saving functions do not have encoding argument and always assume encoding_wchar encoding.

	Note
	The current behavior for Unicode conversion is to skip all invalid UTF sequences during conversion. This behavior should not be relied upon; if your node/attribute names do not contain any valid UTF sequences, they may be output as if they are empty, which will result in malformed XML document.

When you are saving the document using xml_document::save() or xml_document::save_file(), a default XML document declaration is output, if format_no_declaration is not speficied and if the document does not have a declaration node. However, the default declaration is not customizable. If you want to customize the declaration output, you need to create the declaration node yourself.

	Note
	By default the declaration node is not added to the document during parsing. If you just need to preserve the original declaration node, you have to add the flag parse_declaration to the parsing flags; the resulting document will contain the original declaration node, which will be output during saving.

Declaration node is a node with type node_declaration; it behaves like an element node in that it has attributes with values (but it does not have child nodes). Therefore setting custom version, encoding or standalone declaration involves adding attributes and setting attribute values.

This is an example that shows how to create a custom declaration node (samples/save_declaration.cpp):

// get a test document
pugi::xml_document doc;
doc.load("<foo bar='baz'><call>hey</call></foo>");

// add a custom declaration node
pugi::xml_node decl = doc.prepend_child(pugi::node_declaration);
decl.append_attribute("version") = "1.0";
decl.append_attribute("encoding") = "UTF-8";
decl.append_attribute("standalone") = "no";

// <?xml version="1.0" encoding="UTF-8" standalone="no"?> 
// <foo bar="baz">
//         <call>hey</call>
// </foo>
doc.save(std::cout);
std::cout << std::endl;