The most common source of XML data is files; pugixml provides dedicated functions for loading an XML document from file:

xml_parse_result xml_document::load_file(const char* path, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);
xml_parse_result xml_document::load_file(const wchar_t* path, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);

These functions accept the file path as its first argument, and also two optional arguments, which specify parsing options (see Parsing options) and input 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.

load_file destroys the existing document tree and then tries to load the new tree from the specified file. The result of the operation is returned in an xml_parse_result object; this object contains the operation status and the related information (i.e. last successfully parsed position in the input file, if parsing fails). See Handling parsing errors for error handling details.

This is an example of loading XML document from file (samples/load_file.cpp):

pugi::xml_document doc;

pugi::xml_parse_result result = doc.load_file("tree.xml");

std::cout << "Load result: " << result.description() << ", mesh name: " << doc.child("mesh").attribute("name").value() << std::endl;

Sometimes XML data should be loaded from some other source than a file, i.e. HTTP URL; also you may want to load XML data from file using non-standard functions, i.e. to use your virtual file system facilities or to load XML from gzip-compressed files. All these scenarios require loading document from memory. First you should prepare a contiguous memory block with all XML data; then you have to invoke one of buffer loading functions. These functions will handle the necessary encoding conversions, if any, and then will parse the data into the corresponding XML tree. There are several buffer loading functions, which differ in the behavior and thus in performance/memory usage:

xml_parse_result xml_document::load_buffer(const void* contents, size_t size, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);
xml_parse_result xml_document::load_buffer_inplace(void* contents, size_t size, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);
xml_parse_result xml_document::load_buffer_inplace_own(void* contents, size_t size, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);

All functions accept the buffer which is represented by a pointer to XML data, contents, and data size in bytes. Also there are two optional arguments, which specify parsing options (see Parsing options) and input data encoding (see Encodings). The buffer does not have to be zero-terminated.

load_buffer function works with immutable buffer - it does not ever modify the buffer. Because of this restriction it has to create a private buffer and copy XML data to it before parsing (applying encoding conversions if necessary). This copy operation carries a performance penalty, so inplace functions are provided - load_buffer_inplace and load_buffer_inplace_own store the document data in the buffer, modifying it in the process. In order for the document to stay valid, you have to make sure that the buffer's lifetime exceeds that of the tree if you're using inplace functions. In addition to that, load_buffer_inplace does not assume ownership of the buffer, so you'll have to destroy it yourself; load_buffer_inplace_own assumes ownership of the buffer and destroys it once it is not needed. This means that if you're using load_buffer_inplace_own, you have to allocate memory with pugixml allocation function (you can get it via get_memory_allocation_function).

The best way from the performance/memory point of view is to load document using load_buffer_inplace_own; this function has maximum control of the buffer with XML data so it is able to avoid redundant copies and reduce peak memory usage while parsing. This is the recommended function if you have to load the document from memory and performance is critical.

There is also a simple helper function for cases when you want to load the XML document from null-terminated character string:

xml_parse_result xml_document::load_string(const char_t* contents, unsigned int options = parse_default);

It is equivalent to calling load_buffer with size being either strlen(contents) or wcslen(contents) * sizeof(wchar_t), depending on the character type. This function assumes native encoding for input data, so it does not do any encoding conversion. In general, this function is fine for loading small documents from string literals, but has more overhead and less functionality than the buffer loading functions.

This is an example of loading XML document from memory using different functions (samples/load_memory.cpp):

const char source[] = "<mesh name='sphere'><bounds>0 0 1 1</bounds></mesh>";
size_t size = sizeof(source);

// You can use load_buffer to load document from immutable memory block:
pugi::xml_parse_result result = doc.load_buffer(source, size);

// You can use load_buffer_inplace to load document from mutable memory block; the block's lifetime must exceed that of document
char* buffer = new char[size];
memcpy(buffer, source, size);

// The block can be allocated by any method; the block is modified during parsing
pugi::xml_parse_result result = doc.load_buffer_inplace(buffer, size);

// You have to destroy the block yourself after the document is no longer used
delete[] buffer;

// You can use load_buffer_inplace_own to load document from mutable memory block and to pass the ownership of this block
// The block has to be allocated via pugixml allocation function - using i.e. operator new here is incorrect
char* buffer = static_cast<char*>(pugi::get_memory_allocation_function()(size));
memcpy(buffer, source, size);

// The block will be deleted by the document
pugi::xml_parse_result result = doc.load_buffer_inplace_own(buffer, size);

// You can use load to load document from null-terminated strings, for example literals:
pugi::xml_parse_result result = doc.load_string("<mesh name='sphere'><bounds>0 0 1 1</bounds></mesh>");

To enhance interoperability, pugixml provides functions for loading document from any object which implements C++ std::istream interface. This allows you to load documents from any standard C++ stream (i.e. file stream) or any third-party compliant implementation (i.e. Boost Iostreams). There are two functions, one works with narrow character streams, another handles wide character ones:

xml_parse_result xml_document::load(std::istream& stream, unsigned int options = parse_default, xml_encoding encoding = encoding_auto);
xml_parse_result xml_document::load(std::wistream& stream, unsigned int options = parse_default);

load with std::istream argument loads the document from stream from the current read position to the end, treating the stream contents as a byte stream of the specified encoding (with encoding autodetection as necessary). Thus calling xml_document::load on an opened std::ifstream object is equivalent to calling xml_document::load_file.

load with std::wstream argument treats the stream contents as a wide character stream (encoding is always encoding_wchar). Because of this, using load 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 the ability to load documents from non-Unicode encodings, i.e. you can load Shift-JIS encoded data if you set the correct locale.

This is a simple example of loading XML document from file using streams (samples/load_stream.cpp); read the sample code for more complex examples involving wide streams and locales:

std::ifstream stream("weekly-utf-8.xml");
pugi::xml_parse_result result = doc.load(stream);

All document loading functions return the parsing result via xml_parse_result object. It contains parsing status, the offset of last successfully parsed character from the beginning of the source stream, and the encoding of the source stream:

struct xml_parse_result
{
    xml_parse_status status;
    ptrdiff_t offset;
    xml_encoding encoding;

    operator bool() const;
    const char* description() const;
};

Parsing status is represented as the xml_parse_status enumeration and can be one of the following:

description() member function can be used to convert parsing status to a string; the returned message is always in English, so you'll have to write your own function if you need a localized string. However please note that the exact messages returned by description() function may change from version to version, so any complex status handling should be based on status value. Note that description() returns a char string even in PUGIXML_WCHAR_MODE; you'll have to call as_wide to get the wchar_t string.

If parsing failed because the source data was not a valid XML, the resulting tree is not destroyed - despite the fact that load function returns error, you can use the part of the tree that was successfully parsed. Obviously, the last element may have an unexpected name/value; for example, if the attribute value does not end with the necessary quotation mark, like in <node attr="value>some data</node> example, the value of attribute attr will contain the string value>some data</node>.

In addition to the status code, parsing result has an offset member, which contains the offset of last successfully parsed character if parsing failed because of an error in source data; otherwise offset is 0. For parsing efficiency reasons, pugixml does not track the current line during parsing; this offset is in units of pugi::char_t (bytes for character mode, wide characters for wide character mode). Many text editors support 'Go To Position' feature - you can use it to locate the exact error position. Alternatively, if you're loading the document from memory, you can display the error chunk along with the error description (see the example code below).

	Caution
	Offset is calculated in the XML buffer in native encoding; if encoding conversion is performed during parsing, offset can not be used to reliably track the error position.

Parsing result also has an encoding member, which can be used to check that the source data encoding was correctly guessed. It is equal to the exact encoding used during parsing (i.e. with the exact endianness); see Encodings for more information.

Parsing result object can be implicitly converted to bool; if you do not want to handle parsing errors thoroughly, you can just check the return value of load functions as if it was a bool: if (doc.load_file("file.xml")) { ... } else { ... }.

This is an example of handling loading errors (samples/load_error_handling.cpp):

pugi::xml_document doc;
pugi::xml_parse_result result = doc.load_string(source);

if (result)
    std::cout << "XML [" << source << "] parsed without errors, attr value: [" << doc.child("node").attribute("attr").value() << "]\n\n";
else
{
    std::cout << "XML [" << source << "] parsed with errors, attr value: [" << doc.child("node").attribute("attr").value() << "]\n";
    std::cout << "Error description: " << result.description() << "\n";
    std::cout << "Error offset: " << result.offset << " (error at [..." << (source + result.offset) << "]\n\n";
}

All document loading functions accept the optional parameter options. This is a bitmask that customizes the parsing process: you can select the node types that are parsed and various transformations that are performed with the XML text. Disabling certain transformations can improve parsing performance for some documents; however, the code for all transformations is very well optimized, and thus the majority of documents won't get any performance benefit. As a rule of thumb, only modify parsing flags if you want to get some nodes in the document that are excluded by default (i.e. declaration or comment nodes).

	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:

	Caution
	Using in-place parsing (load_buffer_inplace) with parse_fragment flag may result in the loss of the last character of the buffer if it is a part of PCDATA. Since PCDATA values are null-terminated strings, the only way to resolve this is to provide a null-terminated buffer as an input to load_buffer_inplace - i.e. doc.load_buffer_inplace("test\0", 5, pugi::parse_default | pugi::parse_fragment).

These flags control the transformation of tree element contents:

	Note
	parse_wconv_attribute option performs transformations that are required by W3C specification for attributes that are declared as CDATA; parse_wnorm_attribute performs transformations required for NMTOKENS attributes. In the absence of document type declaration all attributes should behave as if they are declared as CDATA, thus parse_wconv_attribute is the default option.

Additionally there are three predefined option masks:

This is an example of using different parsing options (samples/load_options.cpp):

const char* source = "<!--comment--><node>&lt;</node>";

// Parsing with default options; note that comment node is not added to the tree, and entity reference &lt; is expanded
doc.load_string(source);
std::cout << "First node value: [" << doc.first_child().value() << "], node child value: [" << doc.child_value("node") << "]\n";

// Parsing with additional parse_comments option; comment node is now added to the tree
doc.load_string(source, pugi::parse_default | pugi::parse_comments);
std::cout << "First node value: [" << doc.first_child().value() << "], node child value: [" << doc.child_value("node") << "]\n";

// Parsing with additional parse_comments option and without the (default) parse_escapes option; &lt; is not expanded
doc.load_string(source, (pugi::parse_default | pugi::parse_comments) & ~pugi::parse_escapes);
std::cout << "First node value: [" << doc.first_child().value() << "], node child value: [" << doc.child_value("node") << "]\n";

// Parsing with minimal option mask; comment node is not added to the tree, and &lt; is not expanded
doc.load_string(source, pugi::parse_minimal);
std::cout << "First node value: [" << doc.first_child().value() << "], node child value: [" << doc.child_value("node") << "]\n";

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. Most loading functions accept the optional parameter encoding. This is a value of enumeration type xml_encoding, that can have the following values:

The algorithm used for encoding_auto correctly detects any supported Unicode encoding for all well-formed XML documents (since they start with document declaration) and for all other XML documents that start with <; if your XML document does not start with < and has encoding that is different from UTF-8, use the specific encoding.

	Note
	The current behavior for Unicode conversion is to skip all invalid UTF sequences during conversion. This behavior should not be relied upon; moreover, in case no encoding conversion is performed, the invalid sequences are not removed, so you'll get them as is in node/attribute contents.

pugixml is not fully W3C conformant - it can load any valid XML document, but does not perform some well-formedness checks. While considerable effort is made to reject invalid XML documents, some validation is not performed because of performance reasons.

There is only one non-conformant behavior when dealing with valid XML documents: pugixml does not use information supplied in document type declaration for parsing. This means that entities declared in DOCTYPE are not expanded, and all attribute/PCDATA values are always processed in a uniform way that depends only on parsing options.

As for rejecting invalid XML documents, there are a number of incompatibilities with W3C specification, including: