How do I use QRegExp to split an expression

[lni]

Hi,

I need to split string such as "Stage1 <= 4.4e-05 || Stage == 1.2 && Comp >= 1.4e+03 || A+e-C > D" to get all variables in the expression.

In the example string, the result should be "Stage1", "4.4e-05", "Stage", "1.2", "Comp", "1.4e+03", "A", "e", "C", "D"

I am using QRegExp rx( "[+\\-*/(),<>&=| ]" ) to split it.

However, it also split "4.4e-05" and "1.4e+03". How can I write the QRegExp to split it without breaking scientific notation.

Thanks!


Here is sample code

#include <QStringList>
#include <QRegExp>
#include <QDebug>
 
int main()
{
  QString str( "Stage1 <= 4.4e-05 || Stage == 1.2 && Comp >= 1.4e+03 || A+e-C > D" );
  qDebug() << "str =" << str;
 
  QRegExp rx( "[+\\-*/(),<>&=| ]" );
  QStringList strList = str.split( rx, QString::SkipEmptyParts );
 
  qDebug() << "strList =" << strList;
}

#include <QStringList>
#include <QRegExp>
#include <QDebug>

int main()
{
  QString str( "Stage1 <= 4.4e-05 || Stage == 1.2 && Comp >= 1.4e+03 || A+e-C > D" );
  qDebug() << "str =" << str;

  QRegExp rx( "[+\\-*/(),<>&=| ]" );
  QStringList strList = str.split( rx, QString::SkipEmptyParts );

  qDebug() << "strList =" << strList;
}

To copy to clipboard, switch view to plain text mode 

[d_stranz]

You could try making two passes. In the first pass, do not use "+" or "-" in your reg exp. Take the string list result from pass 1 and examine each entry to see if it matches a reg exp for a number (you can search online for suitable regular expressions). If it matches, keep it. If not, then submit the substring to a second pass that splits on your original reg exp in Line 10.

It is hard to write a single regular expression that will match arbitrary string expressions in a single pass. This is why the lex / yacc and flex / bison tools exist.

[lni]

You could try making two passes. In the first pass, do not use "+" or "-" in your reg exp. Take the string list result from pass 1 and examine each entry to see if it matches a reg exp for a number (you can search online for suitable regular expressions). If it matches, keep it. If not, then submit the substring to a second pass that splits on your original reg exp in Line 10.

It is hard to write a single regular expression that will match arbitrary string expressions in a single pass. This is why the lex / yacc and flex / bison tools exist.

I did use two passes, but still fail. I use the following string for test
"a-aa+bb+4.4e-05-1.2e+2"

It should split into "a", "aa", "bb", "4.4e-05", "1.2e+2", but it doesn't. Please help.

Here is my code

#include <QStringList>
#include <QRegExp>
#include <QDebug>
 
static QStringList getFormulaVarList( const QString& formula )
{
  QString::SplitBehavior behavior = QString::SkipEmptyParts;
 
  QRegExp opRx( "[*/()<>&=| ]" );
  QRegExp plusMinus( "[+\\-]" );
 
  QStringList strList;
  foreach( const QString& str, formula.split( opRx, behavior ) ) {
    bool ok;
    str.toDouble( &ok );
    if ( !ok ) {
      strList << str.split( plusMinus, behavior );
    }
  }
  strList.removeDuplicates();
 
  QStringList result;
  foreach( const QString& str, strList ) {
    bool ok;
    str.toDouble( &ok );
    if ( !ok && !str.startsWith( "math.", Qt::CaseInsensitive ) ) {
      result << str;
    }
  }
  result.removeDuplicates();
 
  return result;
 
} // getFormulaVarList
 
int main( int argc, char** argv )
{
  //QString formula( "Stage1 <= 4.4e-05 || Stage == 1.2 && Comp >= 1.4e+03 || A+e-C > D" );
  //QString formula( "a * aa+4.4e-05 + math.log( b )" );
  //QString formula( "a * aa + 4.4e-05 + math.log( b )" );
  QString formula( argv[ 1 ] );
 
  qDebug() << "formula =" << formula;
 
  qDebug() << "items =" << getFormulaVarList( formula );
}

#include <QStringList>
#include <QRegExp>
#include <QDebug>

static QStringList getFormulaVarList( const QString& formula )
{
  QString::SplitBehavior behavior = QString::SkipEmptyParts;

  QRegExp opRx( "[*/()<>&=| ]" );
  QRegExp plusMinus( "[+\\-]" );

  QStringList strList;
  foreach( const QString& str, formula.split( opRx, behavior ) ) {
    bool ok;
    str.toDouble( &ok );
    if ( !ok ) {
      strList << str.split( plusMinus, behavior );
    }
  }
  strList.removeDuplicates();

  QStringList result;
  foreach( const QString& str, strList ) {
    bool ok;
    str.toDouble( &ok );
    if ( !ok && !str.startsWith( "math.", Qt::CaseInsensitive ) ) {
      result << str;
    }
  }
  result.removeDuplicates();

  return result;

} // getFormulaVarList

int main( int argc, char** argv )
{
  //QString formula( "Stage1 <= 4.4e-05 || Stage == 1.2 && Comp >= 1.4e+03 || A+e-C > D" );
  //QString formula( "a * aa+4.4e-05 + math.log( b )" );
  //QString formula( "a * aa + 4.4e-05 + math.log( b )" );
  QString formula( argv[ 1 ] );

  qDebug() << "formula =" << formula;

  qDebug() << "items =" << getFormulaVarList( formula );
}

To copy to clipboard, switch view to plain text mode 

[d_stranz]

I think you should read the documentation on QRegularExpression and especially read the Perl tutorial linked to in that doc. Your regular expressions are much too simple to match the kind of strings you have as input, and I do not think you can do it with a single regular expression.

"a-aa+bb+4.4e-05-1.2e+2"

You might also read this.
You can see that even parsing simple expressions like this one takes a lot of code to recognize the symbols, operators, and constants and convert that into tokens.