WCheckBox help * NEWBIE*
Added by Giovanni Marchetto almost 5 years ago
Hi all!
I've copied the following code from hello World! and i've added only a checkbox for test.
#include <Wt/WApplication.h>
#include <Wt/WBreak.h>
#include <Wt/WContainerWidget.h>
#include <Wt/WLineEdit.h>
#include <Wt/WPushButton.h>
#include <Wt/WText.h>
#include <Wt/WCheckBox.h>
#include <iostream>
class HelloApplication : public Wt::WApplication
{
public:
HelloApplication(const Wt::WEnvironment& env);
private:
Wt::WLineEdit *nameEdit_;
Wt::WText *greeting_;
Wt::WCheckBox *test_;
};
HelloApplication::HelloApplication(const Wt::WEnvironment& env)
: Wt::WApplication(env)
{
setTitle("Hello world");
root()->addWidget(std::make_unique<Wt::WText>("Your name, please? "));
nameEdit_ = root()->addWidget(std::make_unique<Wt::WLineEdit>());
Wt::WPushButton *button = root()->addWidget(std::make_unique<Wt::WPushButton>("Greet me."));
root()->addWidget(std::make_unique<Wt::WBreak>());
Wt::WCheckBox *test_ = root()->addWidget(std::make_unique<Wt::WCheckBox>());
root()->addWidget(std::make_unique<Wt::WBreak>());
greeting_ = root()->addWidget(std::make_unique<Wt::WText>());
auto greet = [this]{
greeting_->setText("Hello there, " + nameEdit_->text());
std::cout << test_->isChecked() << std::endl;
};
button->clicked().connect(greet);
}
int main(int argc, char **argv)
{
return Wt::WRun(argc, argv, [](const Wt::WEnvironment& env) {
return std::make_unique<HelloApplication>(env);
});
}
When i try to compile the code, an error occur on lambda function:
hello.cc: In lambda function:
hello.cc:41:20: error: ‘test_’ is not captured
std::cout << test_->isChecked() << std::endl;
^~~~~
hello.cc:39:23: note: the lambda has no capture-default
auto greet = [this]{
^
hello.cc:33:20: note: ‘Wt::WCheckBox* test_’ declared here
Wt::WCheckBox *test_ = root()->addWidget(std::make_unique<Wt::WCheckBox>());
^~~~~
Thanks for patience.
Replies (2)
RE: WCheckBox help * NEWBIE* - Added by Roel Standaert almost 5 years ago
The lambda function only captures this, which is the HelloApplication, so it can only access members of the HelloApplication, and not local variables, like your test_.
The reason why your test_ is a local variable, and not a member of HelloApplication, is because you are declaring the type again.
If you change this line:
Wt::WCheckBox *test_ = root()->addWidget(std::make_unique<Wt::WCheckBox>());
to this:
test_ = root()->addWidget(std::make_unique<Wt::WCheckBox>());
it should work.
RE: WCheckBox help * NEWBIE* - Added by Giovanni Marchetto almost 5 years ago
Thanks for quick and clear reply, and sorry for this stupid question.
I've see now (with your explanation) , the giant mistake that i had made.
Now it's compile.
Have a nice day and thanks again!