lambda capture syntax

[TheCipo76]

Hi to all,
i have to capture array index and pass it to a slot..
i've read some post about lambda but i can't do it..

//arraySco[i] is a QCheckBox
//connect(arraySco[i], SIGNAL(stateChanged()), this, CambiaMag(i)); //this is the goal
connect(arraySco[i], SIGNAL(stateChanged()), this, [=] () {qDebug() << i;});

generate several errors..
i want capture "i" var and pass it to a SLOT (CambiaMag())
anyone can help me please?

[J.Hilk]

@TheCipo76 said in lambda capture syntax:

connect(arraySco[i], SIGNAL(stateChanged()), this, [=] () {qDebug() << i;});

that won't work, you'll need to use the new function pointer based syntax.

I would correct it for you but I'm missing crucial information.

• pointer to the class instance that has the stateChanged signal
• Name of the class that has the stateChanged signal

[eyllanesc]

@TheCipo76 Use new syntax connection: https://wiki.qt.io/New_Signal_Slot_Syntax

[TheCipo76]

@J-Hilk QCheckBox *arraySco[10];

[J.Hilk]

@TheCipo76

alight

connect(arraySco[i], &QCheckBox::stateChanged, this, [=] ()->void {qDebug() << i;});

in case you want to use the argument, because state changed has an int argument:

connect(arraySco[i], &QCheckBox::stateChanged, this, [=] (int state)->void {qDebug() << i << state;});

[TheCipo76]

@J-Hilk Great! Thank you very much.

[JonB]

@TheCipo76
And just so you know. The capture [=] means "capture all local variables, by value" ([&] would be the same but all by reference). In this case you only need i, so you could have written [i] here, or [i, j, ..] for individual ones. Just so you know if you want to use that or see it elsewhere in examples.