問題描述

我在函數(shù)聲明中多次發(fā)現(xiàn)這些符號(hào)，但我不知道它們是什么意思.

I found these symbols in a function declaration several times, but I don't know what they mean.

示例:

void raccogli_dati(double **& V, double **p, int N) { 
  int ultimo = 3; 
  V = new double * [N/2]; 
  for(int i=0; i < N/2; i++) { 
    V[i] = new double[N/2], std :: clog << "digita " << N/2 - i
                 << " valori per la parte superiore della matrice V: "; 
    for(int j=i; j < N/2; j++) 
      std :: cin >> V[i][j], p[ultimo++][0] = (V[i][j] /= sqrt(p[i][0]*p[j][0]));
  } 
  for(int i=1; i < N/2; i++) 
    for(int j=0; j < i; j++) 
       V[i][j] = V[j][i];
}

推薦答案

即以引用方式取參數(shù).因此，在第一種情況下，您通過引用獲取指針參數(shù)，因此您對指針值所做的任何修改都會(huì)反映在函數(shù)之外.第二個(gè)與第一個(gè)相似，唯一的區(qū)別是它是一個(gè)雙指針.看這個(gè)例子:

That is taking the parameter by reference. So in the first case you are taking a pointer parameter by reference so whatever modification you do to the value of the pointer is reflected outside the function. Second is the simlilar to first one with the only difference being that it is a double pointer. See this example:

void pass_by_value(int* p)
{
    //Allocate memory for int and store the address in p
    p = new int;
}

void pass_by_reference(int*& p)
{
    p = new int;
}

int main()
{
    int* p1 = NULL;
    int* p2 = NULL;

    pass_by_value(p1); //p1 will still be NULL after this call
    pass_by_reference(p2); //p2 's value is changed to point to the newly allocate memory

    return 0;
}

這篇關(guān)于*& 的含義和**&在 C++ 中的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！