Qt Documentation

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QScopeGuard Class

template <typename F> class QScopeGuard

Provides a scope guard for calling a function at the end of a scope. More...

Header: #include <QScopeGuard>
CMake: find_package(Qt6 COMPONENTS Core REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core
Since: Qt 5.12

Public Functions

QScopeGuard(const F &f)
QScopeGuard(F &&f)
void dismiss()
QScopeGuard<typename std::decay<F>::type> qScopeGuard(F &&f)

Detailed Description

QScopeGuard<F> is a class of which the sole purpose is to run the function f in its destructor. This is useful for guaranteeing your cleanup code is executed, whether the function is exited normally, exited early by a return statement, or exited by an exception.

Note: Exceptions are not supported. The callable shouldn't throw when executed, copied or moved.

See also QScopedValueRollback.

Member Function Documentation

QScopeGuard::QScopeGuard(F &&f)

QScopeGuard::QScopeGuard(const F &f)

Create a scope guard that will execute f at the end of the scope.

If F is a lambda, its type cannot be written. In that case you need to either rely on class template argument deduction (C++17 feature) and leave the template parameter out completely or use the helper function qScopeGuard() instead of this constructor.

This function was introduced in Qt 5.15.

void QScopeGuard::dismiss()

Disarms the scope guard, so that the function F will not be called at the end of the scope.

Related Non-Members

template <typename F> QScopeGuard<typename std::decay<F>::type> qScopeGuard(F &&f)

The qScopeGuard function can be used to call a function at the end of the scope.

Create a scope guard that will execute f at the end of the scope.

This helper function is provided so that you can easily construct a QScopeGuard without having to name the template parameter for the type of the callable. If F is a lambda then you cannot write its type and relying on this helper or class template argument deduction is necessary.

Example usage is as follows:

void myComplexCodeWithMultipleReturnPoints(int v)
{
    // The lambda will be executed right before your function returns
    auto cleanup = qScopeGuard([] { code you want executed goes HERE; });

    if (v == -1)
        return;

    int v2 = code_that_might_throw_exceptions();

    if (v2 == -1)
        return;

    (...)
}

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