C++ 如何在构造函数中初始化类的成员数组？
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How to initialise a member array of class in the constructor?
提问by chintan s
I am trying to do the following:
我正在尝试执行以下操作：
class sig
{
public:
int p_list[4];
}
sig :: sig()
{
p_list[4] = {A, B, C, D};
}
I get an error
我收到一个错误
missing expression in the constructor.
构造函数中缺少表达式。
So how do I initilalise an array?
那么如何初始化一个数组呢？
回答by Kerrek SB
In C++11 only:
仅在 C++11 中：
class sig
{
int p_list[4];
sig() : p_list { 1, 2, 3, 4 } { }
};
Pre-11 it was not possible to initialize arrays other than automatic and static ones at block scope or static ones at namespace scope.
在 11 之前，除了块范围内的自动和静态数组或命名空间范围内的静态数组之外，不可能初始化数组。
回答by Konrad Rudolph
So how do I initilalise an array?
那么如何初始化一个数组呢？
Using the normal initialiser list syntax:
使用正常的初始化列表语法：
sig::sig() : p_list{1, 2, 3, 4}
{ }
Note, this only works in C++11. Before that, you need to use a boost::arrayan initialise it inside a function.
请注意，这仅适用于 C++11。在此之前，您需要boost::array在函数内使用初始化它。
回答by Some programmer dude
If your compiler doesn't support C++11 initialization, then you have to assign each field separatly:
如果您的编译器不支持 C++11 初始化，那么您必须单独分配每个字段：
p_list[0] = A;
p_list[1] = B;
p_list[2] = C;
p_list[3] = D;
回答by PaperBirdMaster
If your current compiler doesn't yet support C++11, you can initialize the vector contents using standard algorithms and functors:
如果您当前的编译器还不支持 C++11，您可以使用标准算法和函子初始化向量内容：
class sig
{
public:
sig()
{
struct Functor
{
Functor() : value(0) {};
int operator ()() { return value++; };
int value;
};
std::generate(p_list, p_list + 4, Functor());
}
int p_list[4];
};
Previous snippet example here.
上一个片段示例在这里。
Yes, is kind of ugly (at least, it looks ugly for me) and doesn't do the work at compile time; but it does the work that you need in the constructor.
是的，有点丑（至少，对我来说它看起来很丑）并且在编译时不做这项工作；但它在构造函数中完成了您需要的工作。
If you need some other kind of initialization (initialization with even/odd numbers, initialization with random values, start with anoter value, etc...) you only need to change the Functor, and this is the only advantage of this ugly approach.
如果您需要某种其他类型的初始化（偶数/奇数初始化、随机值初始化、从另一个值开始等），您只需要更改 Functor，这是这种丑陋方法的唯一优势。
回答by Mayur Lokare
You can initialise the array members like this using c++11 compiler using -std=c++11 or -std=gnu++11 option
您可以使用 c++11 编译器使用 -std=c++11 或 -std=gnu++11 选项初始化数组成员
struct student {
private :
int marks[5];
public :
char name[30];
int rollno;
student(int arr[], const char *name, int rno):marks{arr[0], arr[1], arr[2], arr[3], arr[4]}{
strcpy(this->name, name);
this->rollno = rno;
}
void printInfo() {
cout <<"Name : "<<this->name<<endl;
cout <<"Roll No : "<<this->rollno<<endl;
for(int i=0; i< 5; i++ ) {
cout <<"marks : "<<marks[i]<<endl;
}
}
};
int main(int argc, char *argv[]) {
int arr[] = {40,50,55,60,46};
//this dynamic array passing is possible in c++11 so use option -std=c++11
struct student s1(new int[5]{40, 50, 55, 60, 46}, "Mayur", 56);
//can't access the private variable
//cout <<"Mark1 : "<<s1.marks[0]<<endl;
s1.printInfo();`enter code here`
}
回答by Shahzeb
p_list[4] = {'A', 'B', 'C', 'D'};
