Question

我是C ++的新手。这是我的问题。我将总线，步进器声明为h文件中的私有实例：

class Motor_control
{
public:
       ...
private:
    IICBus bus ;
    IICStepper stepper ;
    IICStepper stepper_r ;
    IICStepper stepper_l ;
};

然后在构造函数

中启动它们

Motor_control::Motor_control(){
    IICBus bus ("/dev/i2c-2",0,"");
    IICStepper stepper (bus,0x00, "Global addr");
    IICStepper stepper_r (bus,0x6e, "Stepper Modul");
    IICStepper stepper_l (bus,0x66, "Stepper Modul");
}

IICStepper在.cpp：

中声明

 IICStepper::IICStepper(IICBus& bus, int addr, const string& name) : IICBase(bus,addr, name) { } in cpp

和.h：

class IICStepper : public IICBase { public: IICStepper(IICBus& bus, int addr, const std::string& name); virtual ~IICStepper(){}; ...}

它compalins

       ../src/Motor_control.h:15: error: no matching function for call to 'IICStepper::IICStepper()'
../src/Stepper.h:41: note: candidates are: IICStepper::IICStepper(IICBus&, int, const std::string&)
../src/Stepper.h:38: note:                 IICStepper::IICStepper(const IICStepper&)
../src/Motor_control.h:15: error: no matching function for call to 'IICBus::IICBus()'
../src/Bus.h:28: note: candidates are: IICBus::IICBus(const std::string&, int, const std::string&)
../src/Bus.h:17: note:                 IICBus::IICBus(const IICBus&)
../src/Motor_control.h:15: error: no matching function for call to 'IICStepper::IICStepper()'
../src/Stepper.h:41: note: candidates are: IICStepper::IICStepper(IICBus&, int, const std::string&)
../src/Stepper.h:38: note:                 IICStepper::IICStepper(const IICStepper&)
../src/Motor_control.h:15: error: no matching function for call to 'IICStepper::IICStepper()'
../src/Stepper.h:41: note: candidates are: IICStepper::IICStepper(IICBus&, int, const std::string&)
../src/Stepper.h:38: note:                 IICStepper::IICStepper(const IICStepper&)
../src/Motor_control.h:15: error: no matching function for call to 'IICStepper::IICStepper()'
../src/Stepper.h:41: note: candidates are: IICStepper::IICStepper(IICBus&, int, const std::string&)
../src/Stepper.h:38: note:                 IICStepper::IICStepper(const IICStepper&)

Answer 1

在构造函数体进入之前，将初始化所有用户类型。因为您没有IICStepper的默认构造函数，所以您将收到错误。

您需要使用初始化列表：

Motor_control::Motor_control() : 
   bus("/dev/i2c-2", 0, ""),
   stepper(bus, 0, "Global addr"),
   stepper_r(bus, 0x6e, "Stepper Modul"),
   stepper_l(bus, 0x66, "Stepper Modul") 
{

}

您的版本不仅不会初始化成员，还会创建以后从未使用过的新临时对象。

Answer 2

我最好的猜测是，当你传递一个字符串作为参数时，例如

"Global addr"

，字符串作为'const char *'传递，而不是'const std :: string＆amp;'。从我的角度来看，你只是传递了错误类型的变量。

Answer 3

这是错误的：

Motor_control::Motor_control(){
    IICBus bus ("/dev/i2c-2",0,"");
    IICStepper stepper (bus,0x00, "Global addr");
    IICStepper stepper_r (bus,0x6e, "Stepper Modul");
    IICStepper stepper_l (bus,0x66, "Stepper Modul");
}

上面的代码没有按照您的想法执行。具体来说，它创建了三个局部变量（构造函数的本地变量），其名称与三个其他变量的名称完全相同 - 您的成员变量。此代码不初始化您的成员变量。

您看到的错误消息是由成员变量的默认初始化引起的。要避免默认初始化，必须在初始化列表中列出成员变量，如下所示：

Motor_control::Motor_control() : bus("/dev/i2c-2", 0, ""),
    stepper(bus, 0, "Global addr"),
    stepper_r(bus, 0x6e, "Stepper Modul"),
    stepper_l(bus, 0x66, "Stepper Modul") {
}

用C ++创建对象

3 个答案: