C ++返回数组，数据丢失[重复]

Question

我是来自 Java 的 C++ 新手，所以请原谅我的幼稚，但我试图将数组从函数中传递出去。我知道这样做的方法是传递一个指针，如下所示：

int *foo(){
   int arr[3] = {1, 2, 3};
   int *arrptr = arr;
   return arrptr;
}

然后访问该数组：

int main(){
   int *arrptr = foo();  //create a pointer to array

   //cout all elements
   for(int x = 0; x < 3; x++)
      cout << arrptr[x];

   return 0;
}

当然，这很好用。但是由于某种原因，在不同的代码中，这个相同的过程只返回数组的第一个值，其余的似乎是随机的。

int main(){
   stringstream allstats;
   allstats << readFile(); //readFile() simply returns a string read from a file

   while(!allstats.eof()){     //check for end of stream
      string temp;             
      getline(allstats, temp); //grab a line from allstats and put it into temp

      double *arr = calculateStats(temp); //create pointer to array of stats calculated for temp

      // print arr
      for(int x = 0; x < 6; x++)
         cout << arr[x] << endl;
      //****This spits out the correct value for arr[0] but for the rest of the array
      //****it is values like 8.58079e-306 which tells me those addresses have been
      //****overwritten.

   }
   return 0;
}

//calculate stats for each player, return as formatted string
double* calculateStats(string player){
   //cut for conciseness, just know it works and the proper values are in the following array

   //create stat array
   double statarr[6] = {(double)BA, (double)OB, (double)H, (double)BB, (double)K, (double)HBP};

   //create pointer to stat array
   double *ptr;
   ptr = statarr;

   return ptr;
}

在 Java 中，它就像返回一个数组一样简单，工作就完成了。这在 C++ 中是否可能，或者这超出了我的理解水平并且解决方案比我想象的要复杂得多？

Answer 1

您不能在外部函数中拥有对局部数组的指针引用，因为一旦局部函数退出，它的堆栈可能会被重用，并且局部变量中的数据将包含垃圾。

您可以将单词 static 添加到本地数组声明中，以使其内存在其他函数（和重复调用）中保持不变。虽然这根本不是推荐的解决方案。

变化：

double statarr[6] = {(double)BA, (double)OB, (double)H, (double)BB, (double)K, (double)HBP};

收件人：

static double statarr[6] = {(double)BA, (double)OB, (double)H, (double)BB, (double)K, (double)HBP};

虽然，更好的解决方案是不将数组声明为 calculateStats

类似：

    //calculate stats for each player, return as formatted string
double* calculateStats(string player, double *outArr){
   //cut for conciseness, just know it works and the proper values are in the following array

   //create stat array
   outArr[0] = (double)BA;
   outArr[1] = (double)OB;
   outArr[2] = (double)H;
   outArr[3] = (double)BB;
   outArr[4] = (double)K;
   outArr[5] = (double)HBP;


   return outArr;
}

然后有：

int main(){
   stringstream allstats;
   allstats << readFile(); //readFile() simply returns a string read from a file

   while(!allstats.eof()){     //check for end of stream
      string temp;             
      getline(allstats, temp); //grab a line from allstats and put it into temp

      double arr[6]
      calculateStats(temp, arr) //create pointer to array of stats calculated for temp

      // print arr
      for(int x = 0; x < 6; x++)
         cout << arr[x] << endl;
      //****This spits out the correct value for arr[0] but for the rest of the array
      //****it is values like 8.58079e-306 which tells me those addresses have been
      //****overwritten.

   }
   return 0;
}