Question

让我们说我为一个大小的数组创建了一个模板：

template <int Size>
class SizedArray {
   private:
      std::vector<int> array_;
   public:
      SizedArray() {
         for (int i = 0; i < Size; ++i) {
            array_.push_back(0);
         }
      }
      ... // other methods
};

我想定义一个新功能merge，它会创建一个包含两个SizedArray s

的元素的新SizedArray

template<typename SizeA, typename SizeB>      
SizedArray<SizeA + SizeB> merge(SizedArray<SizeA> a, SizedArray<SizeB> b) {
   // additional code
}

但是，当我尝试编译此代码时，我收到一条错误说＆＃34;模板参数1无效＆＃34; （可能是因为返回类型的SizeA + SizeB部分）。有没有办法创建一个依赖返回类型，它是函数参数的依赖类型的总和？

Answer 1

在您的函数声明中，

package com.ak.gymtimer; import android.annotation.SuppressLint; import android.annotation.TargetApi; import android.os.Build; import android.os.Bundle; import android.os.CountDownTimer; import android.support.design.widget.FloatingActionButton; import android.support.design.widget.Snackbar; import android.support.v7.app.AppCompatActivity; import android.support.v7.widget.Toolbar; import android.view.View; import android.widget.Button; import android.widget.TextView; import java.util.concurrent.TimeUnit; public class CountDown extends AppCompatActivity { long prepTimeInMillis,workTimeInMillis,restTimeInMillis,coolDownTimeInMillis,totalTimeInMillis; int round,roundCount=0; TextView typeV,roundV,totalTimeV,typeSet; CounterClass timer; CounterClass1 timer1; long pausemillis,pauseTotalMillis; int pauseMethodNum; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_count_down); Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar); typeV =(TextView) findViewById(R.id.countDownTime); roundV =(TextView) findViewById(R.id.textView15); totalTimeV =(TextView) findViewById(R.id.totalTimeleft); typeSet =(TextView) findViewById(R.id.textView12); Button pauseBt = (Button) findViewById(R.id.pause); Button cancelBt = (Button) findViewById(R.id.cancel); Button nextBt = (Button) findViewById(R.id.next); Button startBt = (Button) findViewById(R.id.start); prepTimeInMillis = getIntent().getExtras().getLong("prep"); workTimeInMillis = getIntent().getExtras().getLong("work"); restTimeInMillis = getIntent().getExtras().getLong("rest"); coolDownTimeInMillis=getIntent().getExtras().getLong("cooldown"); round = getIntent().getExtras().getInt("round"); totalTimeInMillis=getIntent().getExtras().getLong("total"); System.out.println("Time in Millis"); System.out.println(prepTimeInMillis); System.out.println(workTimeInMillis); System.out.println(restTimeInMillis); System.out.println(coolDownTimeInMillis); System.out.println(round); System.out.println(totalTimeInMillis); if (round == 0){ round = 1; } roundV.setText("1/" + round); timer1 = new CounterClass1(totalTimeInMillis,1000); timer1.start(); preptimeFunc(); pauseBt.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { timer.cancel(); timer1.cancel(); } }); cancelBt.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { timer1.cancel(); timer.cancel(); } }); nextBt.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { timer.start(); timer1.start(); } }); startBt.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { timer = new CounterClass(prepTimeInMillis,pausemillis,pauseMethodNum); timer.start(); timer1 = new CounterClass1(prepTimeInMillis,pauseTotalMillis); timer1.start(); } }); } public void preptimeFunc(){ typeSet.setText("Count Down"); timer = new CounterClass(prepTimeInMillis,1000,1); timer.start(); } public void worktimeFunc(){ typeSet.setText("WorkOut"); roundCount = roundCount + 1; roundV.setText(String.format("%02d",roundCount) + "/" + String.format("%02d",round)); timer = new CounterClass(workTimeInMillis,1000,2); timer.start(); } public void resttimeFunc(){ typeSet.setText("Rest"); timer = new CounterClass(restTimeInMillis,1000,3); timer.start(); } public void cooldowntimeFunc(){ typeSet.setText("Cool Down"); timer = new CounterClass(coolDownTimeInMillis,1000,4); timer.start(); } public class CounterClass extends CountDownTimer { long millis; int methodNum; public CounterClass(long millisInFuture, long countDownInterval,int methodNum1) { super(millisInFuture, countDownInterval); this.millis = millisInFuture; this.methodNum = methodNum1; } @Override public void onFinish() { timer.cancel(); typeV.setText("00:00"); if (methodNum== 1) { worktimeFunc(); } if (methodNum == 2){ resttimeFunc(); } if (methodNum == 3){ if (roundCount < round){ worktimeFunc(); }else { cooldowntimeFunc(); } } } @SuppressLint("NewApi") @TargetApi(Build.VERSION_CODES.GINGERBREAD) @Override public void onTick(long millisUntilFinished) { millis = millisUntilFinished; pausemillis = millis; pauseMethodNum = methodNum; System.out.println(millis); typeV.setText(String.format("%02d",millis/1000)); } } public class CounterClass1 extends CountDownTimer { long millisTotal; public CounterClass1(long millisInFuture, long countDownInterval) { super(millisInFuture, countDownInterval); this.millisTotal = millisInFuture; } @Override public void onFinish() { timer1.cancel(); timer.cancel(); typeV.setText("00:00"); totalTimeV.setText("00:00"); } @SuppressLint("NewApi") @TargetApi(Build.VERSION_CODES.GINGERBREAD) @Override public void onTick(long millisUntilFinished) { millisTotal = millisUntilFinished; System.out.println(millisTotal); pauseTotalMillis = millisTotal; int min = (int) (millisTotal/(1000 * 60)); int sec = (int) ((millisTotal/1000)%60); totalTimeV.setText(String.format("%02d",min) + ":" + String.format("%02d",sec)); } } }和SizeA是SizeB s，而不是typename s。您显然无法添加类型，但如果您将函数的模板参数声明为int，那么事情就会起作用。

返回模板化依赖类型

1 个答案: