Using TLex

The following code fragments show the use of several TLex8 and TLex16 methods. All the code uses the build independent form TLex.

This converts an real number into a string, which is then assigned to a TLex.

TBuf<0x100> convertRealToString;
// want a TLex from a value
if (convertRealToString.Num(value,format) < KErrNone )
    {
       ...
       }
else
    {
    convertRealToString.ZeroTerminate();
    TLex string(convertRealToString) ;
       }

This takes a descriptor as a function parameter, and copies it to a TLex.

TInt RPNCalc(const TDesC& iCommand, TReal& returnValue)
    {
    TLex input (iCommand) ;
       }

This shows a code flow decision made according to next character to be read from the TLex:

if (!(input.Peek()).IsDigit()) // found non-digit after decimal point if

This shows the use of the Inc() function to move past a character that has been peeked:

if (input.Peek() == '-')
    {
    input.Inc() ; // move past minus sign & flag
    negative = ETrue ;
    }

This shows the use of UnGet() to restore the previously "got" character.

....
if (input.Offset() > 0) // if not at start of line
    {
    input.UnGet() ; // restore 'got' character
    }

If the previous character is before the start of the string, then the function raises a USER 59 panic for the TLex8 variant and a USER 64 panic for the TLex16 variant.

This shows how to allow part of a TLex can be parsed again:

if (!(input.Peek()).IsDigit())
    {
    // found non-digit after decimal point. Error, so rewind
    input.UnGetToMark(startMark);
    }

This parses a TLex for the next token:

input.Mark() ; // remember where we are
input.SkipCharacters() ; // move to end of character token
if ( input.TokenLength() != 0 ) // if valid potential token
...

This shows how TokenLength() is used to return the difference between the position of the next character and the extraction mark. This gives a check as to whether the token length is valid. An invalid token length implies an invalid token.

if ( input.TokenLength() != 0 ) // if valid token length
...

This extracts a marked token.

TPtrC token = input.MarkedToken() ; // extract token

This shows how to return the offset of the next character position from the start of the string.

if (input.Offset() > 0) // if not at start of line
    {
    input.UnGet() ; // restore 'got' character
    ...
    }

This example shows how to return the offset of the next character position from the start of the string.

if (input.Val(extractUint) == KErrNone)
    {
    stack.Push(TReal(extractUint)) ;
    }
else
    {
    if (input.Val(extractReal) == KErrNone)
        {
        stack.Push(extractReal) ;
        }
    }

This extracts an unknown number type. Tries an integer first and then, if this fails, tries a real:

if (input.Val(extractUint) == KErrNone)
    stack.Push(TReal(extractUint)) ;
else if (input.Val(extractReal) == KErrNone)
    stack.Push(extractReal) ;