使用命令行参数选择数据类型？

Basically, based on whether a user inputs a 0 or 1 as a command line argument, I want my data class to either have a vector or an array (static) as its data member. I don't believe you can add if statements to .h files, but I'd like to do the following:

基本上,根据用户是否输入0或1作为命令行参数,我希望我的数据类有一个向量或一个数组(静态)作为其数据成员。我不相信你可以在.h文件中添加if语句,但我想做以下事情:

/*A.h*/
//various functions
private:
if(argv[1] == 0)
    vector b;
else if(argv[1] == 1)
    array b[10];

Is there a simple way to do this? Thanks!

有一个简单的方法吗?谢谢!

3 个解决方案

#1

C-type arrays and std::vector have very different interfaces, so even if you were able to do this, it would be tough to write meaningful code, as vector has push_back(), empty(), etc., and arrays do not.

C类型数组和std :: vector有非常不同的接口,所以即使你能够做到这一点,编写有意义的代码也很困难,因为vector有push_back(),empty()等,而数组也有不。

What you are looking for is one object type with a consistent interface, that can have multiple implementations under-the-hood (it can be implemented using a C-style array, or a C++ standard vector). This is called polymorphism and a tutorial of how to achieve this with C++ can be found here: http://www.cplusplus.com/doc/tutorial/polymorphism/

您正在寻找的是具有一致接口的一种对象类型,可以在引擎盖下具有多个实现(可以使用C样式数组或C ++标准向量来实现)。这称为多态,有关如何使用C ++实现此目的的教程可以在这里找到:http://www.cplusplus.com/doc/tutorial/polymorphism/

#2

One way to achieve that would be to use a template helper function. However note that this may lead to much code duplication if the code is complicated. But as I guess it's for something like performance measurement of different implementation methods (why else would the program user care how it is implemented), I guess that the code isn't too complicated anyway.

实现这一目标的一种方法是使用模板辅助函数。但请注意,如果代码很复杂,这可能会导致代码重复。但是我认为这是针对不同实现方法的性能测量(为什么程序用户会如何实现它),我想这个代码并不是太复杂。

So for example:

例如:

template<typename type_to_use> int template_main(int argc, char* argv[])
{
  type_to_use b;
  // ...
}

int main(int argc, char* argv[])
{
  if (argv[1]==0)
    template_main<vector>(argc, argv);
  else
    template_main<int[10]>(argc, argv);
}

#3

Is there a simple way to do this?

有一个简单的方法吗?

Yes: you create two different implementations with a common interface, defined by a base class. Then, you use a class factory to instantiate one of them, based on runtime parameters.

是:您使用由基类定义的公共接口创建两个不同的实现。然后,使用类工厂根据运行时参数实例化其中一个工厂。

class data {
public:
    virtual ~data() = 0;
    // define public interface here
};

class vector_data: public data {
    std::vector<int> values;
public:
    // implement public interface here in terms of values
};

class array_data: public data {
    int values[20]; // or, std::array<int, 10> values;
public:
    // implement public interface here in terms of values
};

std::unique_ptr<data> make_data(bool vector_data)
{
    if(vector_data)
        return { new vector_data() };
    return { new array_data(); }
}

int main(int argc, char* argv[])
{
    std::vector<std::string> args{ argv, argv + argc };
    auto data = make_data( args[1] == "vector" };
}

data will be instantiated to vector data only when you call:

只有在您调用时,数据才会被实例化为矢量数据:

> application.exe vector

#1