标头中的 std::vector 大小 [英] std::vector size in header

问题描述

我有一个关于 std::vector 的小问题.在 main.h 中，我尝试制作固定大小的 int 向量

I have small question about std::vector. In main.h i try to make fixed size int vector

std::vector<int> foo(7);

但是 g++ 给出了这个错误:

But g++ gived this error:

../test/main.h:21:26: error: expected identifier before numeric constant
 std::vector<int> foo(7);
../main/main.h:21:26: error: expected ',' or '...' before numeric constant

如何创建固定大小长度的私有向量变量?或者我应该简单地在构造函数中制作

How can i create private vector variable of fixed size length? Or should i simply make in constructor

for(int i=0; i<7;i++){
    foo.push_back(0);
}

推荐答案

假设 foo 是数据成员，您的语法无效.通常，您可以像这样初始化 T 类型的数据成员:

Assuming foo is a data member, your syntax is invalid. In general, you can initialize a data member of type T like this:

T foo{ctor_args};

或者这个

T foo = T(ctor_args);

然而，std::vector 有一个接受 std::initializer_list 的构造函数，这意味着第一种形式将产生一个大小-1 向量，单个元素值为 7.所以你被困在第二种形式中:

However, std::vector<int> has a constructor that takes an std::initializer_list<int>, which means that the first form would yield a size-1 vector with a single element of value 7. So you are stuck with the second form:

std::vector<int> foo = std::vector<int>(7);

如果您坚持使用 C++11 之前的编译器，则需要使用构造函数:

If you are stuck with a pre-C++11 compiler, you would need to use a constructor:

class bar
{
public:
    bar() : foo(7) {}
private:
  std::vector<int> foo;
};

并注意在所有构造函数中初始化向量(如果适用).

and take care to initialize the vector in all constructors (if applicable.)

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