问题

我正在尝试在另一个实例中初始化一个已定义类的向量，测试代码如下：

```cpp
#include <vector>

class A
{
public:
    float x = 0.0;
};

class B
{
public:
    std::vector<A> b;
};

int main()
{
    B x;
    for (int i = 0; i < 3; i++)
    {
        A y;
        x.b.insert(x.b.begin(), y);
    }
}

但是否有更巧妙的方法来初始化x？也许像这样：

x.b.insert(x.b.begin(), 3, A);
但我得到错误error: expected primary-expression before ‘)’ token。
谢谢

<details>
<summary>英文:</summary>

i am trying to initial a vector of a defined class in another instance, the test code is as:

```cpp
#include &lt;vector&gt;

class A
{
public:
    float x = 0.0;
};

class B
{
public:
    std::vector&lt;A&gt; b;
};

int main()
{
    B x;
    for(int i = 0; i &lt; 3; i++)
    {
        A y;
        x.b.insert(x.b.begin(), y);
    }
       
}

but is there a more brilliant writing for the initial of x?
something maybe like

x.b.insert(x.b.begin(), 3, A);
which i got error error: expected primary-expression before ‘)’ token
thx

edit: sorry, edited for a better example

答案1

得分: 1

不需要循环或insert，只需构造向量并赋值

B.x = std::vector<A>(3);

或者如果你有特定的值

A y = something;
B.x = std::vector<A>(3, y);

也许这段代码应该放在B的构造函数中。

B.x = std::vector<A>(3);

A y = something;
B.x = std::vector<A>(3, y);