First Tutorial: Make it Run

This tutorial assumes you already have descent_xml and libadt set up in your environment.

This program will be the basis for future tutorials.

It will:

• initialize a token from an XML string
• tests that the XML is a valid XML document
• iterate the token from the beginning of the XML to the end
• exit the program

Save it to a file called noop-example.c and compile with cc -o noop-example noop-example.c -ldescent_xmlstatic.

#include <libadt/str.h>
#include <descent-xml.h>
 
typedef struct descent_xml_lex lex_t;
 
#define str libadt_str_literal
 
#define lex descent_xml_lex_init
#define eof descent_xml_classifier_eof
#define unexpected descent_xml_classifier_unexpected
#define error descent_xml_parse_error
#define parse descent_xml_parse_cstr
#define valid descent_xml_validate_document
 
static int is_end_type(lex_t token)
{
    return token.type == eof;
}
 
static int is_error_type(lex_t token)
{
    return token.type == unexpected
        || token.type == error;
}
 
int main()
{
    lex_t token = lex(str("<element>Hello, world!</element>"));
    if (!valid(token))
        return 1;
 
    while (!is_end_type(token)) {
        if (is_error_type(token)) {
            // Handle error
            return 1;
        }
 
        token = parse(token, NULL, NULL, NULL);
    }
}

The program includes a pretty long preamble, which just removes namespacing noise from libadt and descent_xml functions and data types.

Otherwise, we've defined a few functions for convenience:

• is_end_type checks if the token given to it reflects an end-of-file
• is_error_type checks if the token given is of one of two error types:
  • descent_xml_classifier_unexpected means the lexer encountered a character in an unexpected location (for example, an end-of-file inside an element started with <)
  • descent_xml_parse_error means that the parser encountered an error unrelated to the document. For example, the C-string parsing interface allocates memory to copy values, which can fail.

Once you've gotten the program to compile and run, you can progress on to Second Tutorial: A Simple Printer.