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qtokenautomaton is a token generator, that generates a simple, Unicode aware
tokenizer for C++ that uses the Qt API.
Introduction
=====================
QTokenAutomaton generates a C++ class that essentially has this interface:
class YourTokenizer
{
protected:
enum Token
{
A,
B,
C,
NoKeyword
};
static inline Token toToken(const QString &string);
static inline Token toToken(const QStringRef &string);
static Token toToken(const QChar *data, int length);
static QString toString(Token token);
};
When calling toToken(), the tokenizer returns the enum value corresponding to
the string. This is done with O(N) time complexity, where N is the length of
the string. The returned value can then subsequently be efficiently switched
over. The alternatives, either a long chain of if statements comparing one
QString to several other QStrings; or inserting all strings first into a hash,
are less efficient.
For instance, the latter case of using a hash would involve when excluding the
initial populating of the hash, O(N) + O(1) where 0(1) is assumed to be a
non-conflicting hash lookup.
toString(), which returns the string for the token that an enum value
represents, is implemented to store the strings in an efficient manner.
A typical usage scenario is in combination with QXmlStreamReader. When parsing
a certain format, for instance XHTML, each element name, body, span, table and
so forth, typically needs special treatment. QTokenAutomaton conceptually cuts
the string comparisons down to one.
Beyond efficiency, QTokenAutomaton also increases type safety, since C++
identifiers are used instead of string literals.
Usage
=====================
Using it is approached as follows:
1. Create a token file. Use exampleFile.xml as a template.
2. Make sure it is valid by validating against qtokenautomaton.xsd. On
Linux, this can be achieved by running `xmllint --noout
--schema qtokenautomaton.xsd yourFile.xml`
3. Produce the C++ files by invoking the stylesheet with an XSL-T 2.0
processor[1], for example Saxon.
If the Java SDK is installed, it can be invoked by:
java net.sf.saxon.Transform -xsl:qautomaton2cpp.xsl yourFile.xml
Debian provides a command line utility saxonb-xslt for this:
sudo apt-get install libsaxonb-java
saxonb-xslt -ext:on -xsl:qautomaton2cpp.xsl -s:yourFile.xml
The script regenerate.sh is provided to do this.
4. Include the produced C++ files with your build system.
1.
In Qt there is as of 4.4 no support for XSL-T.
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