Qt setFilter searching? [duplicate] - c++

Question

I have a problem with printing in Qt.
I have HTML code in QString variables. In this code I want to insert data from a database.
I get an error:
E:\apprendreQt\gestionstock6\vente.cpp:117: error: invalid operands of types
'const char*' and 'const char [27]' to binary 'operator+'
How can I fix this?
Here is my code:
int num_bl = ui->numeroBLlineEdit->text().toInt() ;
QString html;
QString requette = "select num_facture,date,nom,prenom,code_fiscale,designation,qte_out, prix,(qte_out * prix ) as Montant, sum(qte_out * prix) as Total from ventes join produits_en_ventes join clients join produits on ventes.vente_id = produits_en_ventes.vente_id and ventes.client_id = clients.client_id and produits_en_ventes.produit_id = produits.produit_id where ventes.client_id = :client_id ";
if(!m_db->isOpen())
QMessageBox::critical(this,tr("Inventoria Solution"),m_db->lastError().text()) ;
else{
m_query->clear();
m_query->prepare(requette);
m_query->bindValue(":client_id ", num_bl);
if(!m_query->exec())
QMessageBox::critical(this,tr("Inventoria Solution"),m_query->lastError().text()) ;
else{
html += " <table>"
"<thead>"
"<tr>"
"<th>N°</th>"
"<th>Désignation</th>"
"<th>Qte</th>"
"<th>Prix Unitaire</th>"
"<th>Montant</th>"
" </tr>"
"</thead>";
while(m_query->next())
{
int num_article = 1;
html += "<tr> <td>" + num_article + "</td> <td>"+m_query->value(5).toString()+"</td> <td>"+m_query->value(6).toInt() + "</td> <td>"+m_query->value(7).toInt() + "</td> <td>" + m_query->value(8).toInt() + "</td></tr>";
num_article++;
}
html += "<tfoot>"
"<tr>"
"<td>Total:"+ m_query->value(9).toInt()+"</td>"
"</tr>"
"</tfoot>"
"</table>";
}
print_Html(html);
}

Answer 1

I'm not sure about your error. However, AFAIK a Qstring cannot be concatenated with an int as such.
int myInt = 0;
QString text = "someString" + myInt; // WRONG
int myInt = 0;
QString text = "someString" + QString::number( myInt ); // CORRECT
or
int myInt = 0;
QString text = "someString" % QString::number( myInt ); // CORRECT

Answer 2

If you use operator+, you need to provide QString as an argument, but you use integer values instead: html += "<tr> <td>" + num_article, where num_article is declared as integer. You can replace it with, for example: QString::number(num_article). The same in this line:
"<td>Total:"+ m_query->value(9).toInt()+"</td>"
should be replaced with
"<td>Total:"+ m_query->value(9).toString()+"</td>"

Answer 3

in Qt5 you can use the QStringLiteral macro for each string that doesn't need to be localized to transform all the string literals from const char* (the C++ default) into QString, this will also make creation of those QStrings cheaper (on compilers that support it)
for Qt4 you can use the QString(const char*) constructor or QString::fromAscii(const char*) static function