C++ Vector 不是包含所有内容的 std 成员

Vector is not a member of std with everything included

提问by Scholar

I'm getting a very strange error and something I've never experienced before, I'm trying to initialize a vector at declaration like so:

我遇到了一个非常奇怪的错误和我以前从未经历过的错误，我试图在声明时初始化一个向量，如下所示：

  vector <int> myVector (5,4,3,4); 

It gives me an error saying that it cannot find a call matching that function, however, if I plug in only 2 numbers it doesn't give me an error.

它给我一个错误，说它找不到匹配该函数的调用，但是，如果我只插入 2 个数字，它不会给我一个错误。

Upon further investigation, even this piece of code throws that vector is not a member of std or that myVector is not a type when I try to call

经过进一步调查，当我尝试调用时，即使是这段代码也会抛出该 vector 不是 std 的成员或 myVector 不是一种类型

myVector.push_back(4);

Now here is the code that gives me the vector is not a member of std, not matching function found, of that nature...

现在这是给我的代码，向量不是 std 的成员，没有找到匹配的函数，具有这种性质......

#include <vector>

using std::vector;

const std::vector<int> newvector;
std::newvector.push_back(5);

int main()
{
}

Error given: newvector in namespace std does not name a type

给出错误：命名空间 std 中的 newvector 未命名类型

采纳答案by Cheers and hth. - Alf

Regarding the final code example,

关于最终的代码示例，

you can't have this statement outside a function body:

你不能在函数体之外有这个语句：

std::newvector.push_back(5);

Place it in main's function body, andremove the std::prefix.

将其放在main的函数体中，并删除std::前缀。

Also note that for this vector modification to be possible, the vector can't be const.

另请注意，要使此向量修改成为可能，向量不能为const。

---

---

Initialization with round parentheses provides arguments to a constructor for the class. There must be a corresponding constructor. And there is no std::vectorconstructor that corresponds to the four arguments in

用圆括号初始化为类的构造函数提供参数。必须有相应的构造函数。并且没有std::vector对应于中的四个参数的构造函数

vector <int> myVector (5,4,3,4); 

Instead do

而是做

vector <int> myVector = {5,4,3,4};

If your compiler supports this C++11 syntax, that is.

如果您的编译器支持这种 C++11 语法，那就是。

If not, then the C++03 way would be

如果没有，那么 C++03 的方式将是

static int const data[] = {5,4,3,4};
static int const n_items = sizeof(data)/sizeof(data[0]);

vector <int> myVector( data, data + n_items );

回答by taocp

std::newvector.push_back(5);

since newvectoris a variable, it is not in namespace std.

因为newvector是一个变量，所以它不在 namespace 中std。

For this case:

对于这种情况：

vector <int> myVector (5,4,3,4); 

If you only use two values (5,4)in this case, it will create a vector with size 5 and each of the elements initialized to 4 (one form of vector construction). If you need to initialize a vector with a list of values, you may try uniform initialization since C++11 as follows:

如果(5,4)在这种情况下只使用两个值，它将创建一个大小为 5 的向量，并且每个元素都初始化为 4（向量构造的一种形式）。如果您需要使用值列表初始化向量，您可以尝试从 C++11 开始的统一初始化，如下所示：

std::vector <int> myVector{5,4,3,4};

Some example of uniform initializationcan be found here: uniform initialization and other C++11 features

uniform initialization可以在此处找到一些示例：uniform Initialization and other C++11 features

回答by 4pie0

There are two issues with this code.

这段代码有两个问题。

1. using std::vector;brings a vectorfrom namespace stdbut you have to use this as follows:

   std::vector<int> newvector;
   newvector.push_back(5);
   

2. You can notice that const dissapeared. This is because you want to change vector at last, so it cannot be const, it would be compile error to call a push_backon it otherwise.

1. using std::vector;带来一个vectorfrom 命名空间，std但您必须按如下方式使用它：

   std::vector<int> newvector;
   newvector.push_back(5);
   

2. 你可以注意到 const 消失了。这是因为你最后想改变vector，所以它不能const，push_back否则调用a会编译错误。

Finally, this should be:

最后，这应该是：

#include <vector>
using std::vector;

int main() {
  std::vector<int> newvector;
  newvector.push_back(5);
  std::vector<int> newvector;
  return 0;
}

回答by yizzlez

The second error, you cannot initialize a vectorwith its elements in the constructor, you must use its initializer list (C++11 only)

第二个错误，您无法vector在构造函数中使用其元素初始化 a ，您必须使用其初始化列表（仅限 C++11）

vector <int> myVector = {5,4,3,4};