expr.tex

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\section{\class{wxExpr}}\label{wxexpr}

The {\bf wxExpr} class is the building brick of expressions similar to Prolog
clauses, or objects. It can represent an expression of type long integer, float, string, word,
or list, and lists can be nested.

\wxheading{Derived from}

None

\wxheading{Include files}

<wx/wxexpr.h>

\wxheading{See also}

\helpref{wxExpr overview}{exproverview}, \helpref{wxExprDatabase}{wxexprdatabase}

\latexignore{\rtfignore{\wxheading{Members}}}

\membersection{wxExpr::wxExpr}\label{wxexprconstr}

\func{}{wxExpr}{\param{const wxString\&}{functor}}

Construct a new clause with this form, supplying the functor name. A clause is an object
that will appear in the data file, with a list of attribute/value pairs.

\func{}{wxExpr}{\param{wxExprType}{ type}, \param{const wxString\&}{ wordOrString = ``"}}

Construct a new empty list, or a word (will be output with no quotes), or a string, depending on the
value of {\it type}.

{\it type} can be {\bf wxExprList}, {\bf wxExprWord}, or {\bf wxExprString}. If {\it type} is wxExprList,
the value of {\it wordOrString} will be ignored.

\func{}{wxExpr}{\param{long}{ value}}

Construct an integer expression.

\func{}{wxExpr}{\param{float}{ value}}

Construct a floating point expression.

\func{}{wxExpr}{\param{wxList* }{value}}

Construct a list expression. The list's nodes' data should
themselves be {\bf wxExpr}s.

wxExpr no longer uses the {\bf wxList} internally,
so this constructor turns the list into its internal
format (assuming a non-nested list) and then deletes the supplied
list.

\membersection{wxExpr::\destruct{wxExpr}}

\func{}{\destruct{wxExpr}}{\void}

Destructor.

\membersection{wxExpr::AddAttributeValue}\label{wxexpraddattributevalue}

Use these on clauses ONLY. Note that the functions for adding strings
and words must be differentiated by function name which is why
they are missing from this group (see \helpref{wxExpr::AddAttributeValueString}{wxexpraddattributevaluestring} and
\rtfsp\helpref{wxExpr::AddAttributeValueWord}{wxexpraddattributevalueword}).

\func{void}{AddAttributeValue}{\param{const wxString\&}{ attribute}, \param{float }{value}}

Adds an attribute and floating point value pair to the clause.

\func{void}{AddAttributeValue}{\param{const wxString\&}{ attribute}, \param{long }{value}}

Adds an attribute and long integer value pair to the clause.

\func{void}{AddAttributeValue}{\param{const wxString\&}{ attribute}, \param{wxList* }{value}}

Adds an attribute and list value pair to the clause, converting the list into
internal form and then deleting {\bf value}. Note that the list should not contain
nested lists (except if in internal {\bf wxExpr} form.)

\func{void}{AddAttributeValue}{\param{const wxString\&}{ attribute}, \param{wxExpr* }{value}}

Adds an attribute and wxExpr value pair to the clause. Do not delete\rtfsp
{\it value} once this function has been called.

\membersection{wxExpr::AddAttributeValueString}\label{wxexpraddattributevaluestring}

\func{void}{AddAttributeValueString}{\param{const wxString\&}{ attribute}, \param{const wxString\&}{ value}}

Adds an attribute and string value pair to the clause.

\membersection{wxExpr::AddAttributeValueStringList}\label{wxexpraddattributevaluestringlist}

\func{void}{AddAttributeValueStringList}{\param{const wxString\&}{ attribute}, \param{wxList* }{value}}

Adds an attribute and string list value pair to the clause.

Note that the list passed to this function is a list of strings, NOT a list
of {\bf wxExpr}s; it gets turned into a list of {\bf wxExpr}s
automatically. This is a convenience function, since lists of strings
are often manipulated in C++.

\membersection{wxExpr::AddAttributeValueWord}\label{wxexpraddattributevalueword}

\func{void}{AddAttributeValueWord}{\param{const wxString\&}{ attribute}, \param{const wxString\&}{ value}}

Adds an attribute and word value pair to the clause.

\membersection{wxExpr::Append}\label{wxexprappend}

\func{void}{Append}{\param{wxExpr*}{ value}}

Append the {\bf value} to the end of the list. `this' must be a list.

\membersection{wxExpr::Arg}\label{wxexprarg}

\constfunc{wxExpr* }{Arg}{\param{wxExprType}{ type}, \param{int}{ n}}

Get nth arg of the given clause (starting from 1). NULL is returned if
the expression is not a clause, or {\it n} is invalid, or the given type
does not match the actual type. See also \helpref{wxExpr::Nth}{wxexprnth}.

\membersection{wxExpr::Insert}\label{wxexprinsert}

\func{void}{Insert}{\param{wxExpr* }{value}}

Insert the {\bf value} at the start of the list. `this' must be a list.

\membersection{wxExpr::GetAttributeValue}\label{wxexprgetattributevalue}

These functions are the easiest way to retrieve attribute values, by
passing a pointer to variable. If the attribute is present, the
variable will be filled with the appropriate value.  If not, the
existing value is left alone.  This style of retrieving attributes
makes it easy to set variables to default values before calling these
functions; no code is necessary to check whether the attribute is
present or not.

\constfunc{bool}{GetAttributeValue}{\param{const wxString\&}{ attribute}, \param{wxString\&}{ value}}

Retrieve a string (or word) value.

\constfunc{bool}{GetAttributeValue}{\param{const wxString\&}{ attribute}, \param{float\& }{value}}

Retrieve a floating point value.

\constfunc{bool}{GetAttributeValue}{\param{const wxString\&}{ attribute}, \param{int\& }{value}}

Retrieve an integer value.

\constfunc{bool}{GetAttributeValue}{\param{const wxString\&}{ attribute}, \param{long\& }{value}}

Retrieve a long integer value.

\constfunc{bool}{GetAttributeValue}{\param{const wxString\&}{ attribute}, \param{wxExpr**}{ value}}

Retrieve a wxExpr pointer.

\membersection{wxExpr::GetAttributeValueStringList}\label{wxexprgetattributestringlist}

\constfunc{void}{GetAttributeValueStringList}{\param{const wxString\&}{attribute}, \param{wxList* }{value}}

Use this on clauses ONLY. See above for comments on this style of
attribute value retrieval. This function expects to receive a pointer to
a new list (created by the calling application); it will append strings
to the list if the attribute is present in the clause.

\membersection{wxExpr::AttributeValue}\label{wxexprattributevalue}

\constfunc{wxExpr*}{AttributeValue}{\param{const wxString\&}{ word}}

Use this on clauses ONLY. Searches the clause for an attribute
matching {\it word}, and returns the value associated with it.

\membersection{wxExpr::Copy}\label{wxexprcopy}

\constfunc{wxExpr*}{Copy}{\void}

Recursively copies the expression, allocating new storage space.

\membersection{wxExpr::DeleteAttributeValue}\label{wxexprdeletattributevalue}

\func{void}{DeleteAttributeValue}{\param{const wxString\&}{ attribute}}

Use this on clauses only. Deletes the attribute and its value (if any) from the
clause.

\membersection{wxExpr::Functor}\label{wxexprfunctor}

\constfunc{wxString}{Functor}{\void}

Use this on clauses only. Returns the clause's functor (object name).

\membersection{wxExpr::GetClientData}\label{wxexprgetclientdata}

\constfunc{wxObject*}{GetClientData}{\void}

Retrieve arbitrary data stored with this clause. This can be useful when
reading in data for storing a pointer to the C++ object, so when another
clause makes a reference to this clause, its C++ object can be retrieved.
See \helpref{wxExpr::SetClientData}{wxexprsetclientdata}.

\membersection{wxExpr::GetFirst}\label{wxexprgetfirst}

\constfunc{wxExpr*}{GetFirst}{\void}

If this is a list expression (or clause), gets the first element in the list.

See also \helpref{wxExpr::GetLast}{wxexprgetlast}, \helpref{wxExpr::GetNext}{wxexprgetnext}, \helpref{wxExpr::Nth}{wxexprnth}.

\membersection{wxExpr::GetLast}\label{wxexprgetlast}

\constfunc{wxExpr*}{GetLast}{\void}

If this is a list expression (or clause), gets the last element in the list.

See also \helpref{wxExpr::GetFirst}{wxexprgetfirst}, \helpref{wxExpr::GetNext}{wxexprgetnext}, \helpref{wxExpr::Nth}{wxexprnth}.

\membersection{wxExpr::GetNext}\label{wxexprgetnext}

\constfunc{wxExpr*}{GetNext}{\void}

If this is a node in a list (any wxExpr may be a node in a list), gets the
next element in the list.

See also \helpref{wxExpr::GetFirst}{wxexprgetfirst}, \helpref{wxExpr::GetLast}{wxexprgetlast}, \helpref{wxExpr::Nth}{wxexprnth}.

\membersection{wxExpr::IntegerValue}\label{wxexprintegervalue}

\constfunc{long}{IntegerValue}{\void}

Returns the integer value of the expression.

\membersection{wxExpr::Nth}\label{wxexprnth}

\constfunc{wxExpr*}{Nth}{\param{int}{ n}}

Get nth arg of the given list expression (starting from 0). NULL is returned if
the expression is not a list expression, or {\it n} is invalid. See also \helpref{wxExpr::Arg}{wxexprarg}.

Normally, you would use attribute-value pairs to add and retrieve data
from objects (clauses) in a data file. However, if the data gets complex,
you may need to store attribute values as lists, and pick them apart
yourself.

\membersection{wxExpr::RealValue}\label{wxexprrealvalue}

\constfunc{float}{RealValue}{\void}