在C ++中，何時以及如何使用回調(diào)函數(shù)？編輯：我想看一個簡單的例子來編寫一個回調(diào)函數(shù)
3 回答
陪伴而非守候
TA貢獻(xiàn)1757條經(jīng)驗 獲得超8個贊
還有執(zhí)行回調(diào)的C方法：函數(shù)指針
//Define a type for the callback signature,
//it is not necessary, but makes life easier
//Function pointer called CallbackType that takes a float
//and returns an int
typedef int (*CallbackType)(float);
void DoWork(CallbackType callback)
{
float variable = 0.0f;
//Do calculations
//Call the callback with the variable, and retrieve the
//result
int result = callback(variable);
//Do something with the result
}
int SomeCallback(float variable)
{
int result;
//Interpret variable
return result;
}
int main(int argc, char ** argv)
{
//Pass in SomeCallback to the DoWork
DoWork(&SomeCallback);
}
現(xiàn)在，如果您希望將類方法作為回調(diào)傳遞，則這些函數(shù)指針的聲明具有更復(fù)雜的聲明，例如：
//Declaration:
typedef int (ClassName::*CallbackType)(float);
//This method performs work using an object instance
void DoWorkObject(CallbackType callback)
{
//Class instance to invoke it through
ClassName objectInstance;
//Invocation
int result = (objectInstance.*callback)(1.0f);
}
//This method performs work using an object pointer
void DoWorkPointer(CallbackType callback)
{
//Class pointer to invoke it through
ClassName * pointerInstance;
//Invocation
int result = (pointerInstance->*callback)(1.0f);
}
int main(int argc, char ** argv)
{
//Pass in SomeCallback to the DoWork
DoWorkObject(&ClassName::Method);
DoWorkPointer(&ClassName::Method);
}
白衣染霜花
TA貢獻(xiàn)1796條經(jīng)驗 獲得超10個贊
Scott Meyers舉了一個很好的例子：
class GameCharacter;
int defaultHealthCalc(const GameCharacter& gc);
class GameCharacter
{
public:
typedef std::function<int (const GameCharacter&)> HealthCalcFunc;
explicit GameCharacter(HealthCalcFunc hcf = defaultHealthCalc)
: healthFunc(hcf)
{ }
int healthValue() const { return healthFunc(*this); }
private:
HealthCalcFunc healthFunc;
};
我認(rèn)為這個例子說明了一切。
std::function<> 是編寫C ++回調(diào)的“現(xiàn)代”方法。
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