现象

信号发送者找不到正确的信号函数

connect(ui->LSpinBox,&QSpinBox::valueChanged,ui->hSlider,&QSlider::setValue);

QSpinBox的valueChanged函数分为int和QString两种，存在函数重载，需让编译器加以区分。
不区分的话会爆出：

error: C2664: 
“QMetaObject::Connection QObject::connect(const QObject *,const char *,const char *,Qt::ConnectionType) const”: 
无法将参数 2 从“overloaded-function”转换为“const char *”

解决方案

使用QOverload

Qt5官方文档推荐使用的方式

 connect(comboBox, QOverload<int>::of(&QComboBox::activated),[=](int index){ /* ... */ });connect(comboBox, QOverload<const QString &>::of(&QComboBox::activated),[=](const QString &text){ /* ... */ });

auto qOverload(T functionPointer)
Returns a pointer to an overloaded function. The template parameter is the list of the argument types of the function. functionPointer is the pointer to the (member) function:struct Foo {void overloadedFunction();void overloadedFunction(int, const QString &);};... qOverload<>(&Foo::overloadedFunction)... qOverload<int, const QString &>(&Foo::overloadedFunction)
If a member function is also const-overloaded qConstOverload and qNonConstOverload need to be used.
qOverload() requires C++14 enabled. In C++11-only code, the helper classes QOverload, QConstOverload, and QNonConstOverload can be used directly:... QOverload<>::of(&Foo::overloadedFunction)... QOverload<int, const QString &>::of(&Foo::overloadedFunction)
Note: Qt detects the necessary C++14 compiler support by way of the feature test recommendations from C++ Committee's Standing Document 6.
This function was introduced in Qt 5.7.
See also qConstOverload(), qNonConstOverload(), and Differences between String-Based and Functor-Based Connections.

使用指针

创建一个函数指针用于保存指定的函数地址：

void (QComboBox:: * activatedInt)(int) = &QComboBox::activated;
void (QComboBox:: * activatedString)(QString) = &QComboBox::activated;connect(comboBox, activatedInt,[=](int index){ /* ... */ });connect(comboBox, activatedString,[=](const QString &text){ /* ... */ });