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Expat

Expat is a parser library written in C. It is stream-oriented, open-source, and used in the Apache HTTP Server, Mozilla, Perl, Python, and PHP, among many other languages and applications.

Expat is a non-validating, event-driven parser in the style of SAX: it reports parsing events, such as element starts and ends and character data, to application-registered callback (handler) functions as it streams through the document, without checking the document against a DTD or other schema beyond well-formedness. Originally written by James Clark, it is maintained today as libexpat and distributed under the MIT license.

Because it is a small, portable C library, Expat is commonly embedded in other languages via bindings, such as Python's xml.parsers.expat module and PHP's ext/xml extension, rather than used directly by application code.

LanguageC
Processing modelStream-oriented, event-driven (SAX-style)
ValidationNon-validating; checks well-formedness only
LicenseOpen source (MIT license)
Notable usersApache HTTP Server, Mozilla, Perl, Python, PHP, and others

#include <expat.h>
#include <stdio.h>

static void startElement(void *data, const char *name, const char **attr) {
    printf("<%s>\n", name);
}

static void endElement(void *data, const char *name) {
    printf("</%s>\n", name);
}

int main() {
    XML_Parser parser = XML_ParserCreate(NULL);
    XML_SetElementHandler(parser, startElement, endElement);

    /* XML_Parse(parser, buffer, length, isFinal); */

    XML_ParserFree(parser);
    return 0;
}