I have tried this. But it doesn't work.
Qt Code: 
  1. QVector<QTextLength> columnWidth;
  2.   for(int i=0; i<15; i++)
  3.   { 
  4.     if(i==0) 
  5.       columnWidth.append(QTextLength::QTextLength(QTextLength::FixedLength,174));
  6.     if(i>0 && i<10)
  7.       columnWidth.append(QTextLength::QTextLength(QTextLength::FixedLength, 42.25));
  8.     else if(i>9 && i<12)
  9.       columnWidth.append(QTextLength::QTextLength(QTextLength::FixedLength, 118));
  10.     else if(i==12 || i==14)
  11.       columnWidth.append(QTextLength::QTextLength(QTextLength::FixedLength, 100));
  12.     else if(i==13)
  13.       columnWidth.append(QTextLength::QTextLength(QTextLength::FixedLength, 70));
  14.   }
  15.  
  16.   QTextTableFormat numberTableFormat;
  17.   numberTableFormat.setBorder(0);
  18.   numberTableFormat.setCellSpacing(-1);
  19.   numberTableFormat.setColumnWidthConstraints(columnWidth);
  20.   QBrush brush(Qt::black);
  21.   numberTableFormat.setBorderBrush(brush);
  22.   numberTableFormat.setBorderStyle(QTextFrameFormat::BorderStyle_Solid);
  23.  //UPDATE 
  24.  numberTableFormat.setWidth(824.25);
  25.  
  26.   QTextTable *mainTable = cursor.insertTable(32, 15, numberTableFormat);
  27.   //SECOND OPTION:
  28.   //mainTable->format().setWidth(824.25);
  29.   cursor = mainTable->cellAt(0,2).firstCursorPosition();
  30.   QTextFrameFormat tempFormat = cursor.currentFrame()->frameFormat();
  31.   tempFormat.setBorder(1);
  32.   cursor.insertFrame(tempFormat);
  33.   cursor.insertText("1");
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