在比较函数内使用非静态类成员 [英] Using a non-static class member inside a comparison function
问题描述
我目前正在开发一个语法分析器类,需要在代码的一点,以排序结构,保存操作符的信息。每个操作符都有一个优先级,这是用户通过我的分析器类的公共成员函数定义的。因此,当排序时,我需要我的排序功能,基于相应的运算符的优先级排序元素。我使用以下代码比较元素:
I'm currently developing a syntaxic analyser class that needs, at a point of the code, to sort structs holding info about operators. Each operator has a priority, which is user-defined through public member functions of my analyser class. Thus, when sorting, I need my sorting function to order elements based on the priority of the corresponding operator. I'm using the following code to compare elements:
bool parser::op_comp(const op_info& o1, const op_info& o2) {
op_def& op1 = operators[o1.op_char];
op_def& op2 = operators[o2.op_char];
return op1.priority > op2.priority;
}
注意,我不得不使这个函数是静态的,因为它定义在类。
Note that I had to make this function static, since it's defined inside of a class.
事实上,我的比较函数比较类型 op_char
的元素,映射包含 op_def
类型的元素,其中有一个字段priority。
In fact, my compare function compares elements of type op_char
, and I retrieve the operator def from a map which contain elements of type op_def
, which have a field "priority".
是我不能管理使用 std :: sort(ops.begin(),ops.end(),std :: mem_fun_ref(& parser :: op_comp))
(其中ops是向量的op_info)
方法。我得到以下错误,这听起来很合乎逻辑:
The problem I'm facing is that I can't manage to use std::sort(ops.begin(), ops.end(), std::mem_fun_ref(&parser::op_comp))
(where ops is a vector of op_info)
method. I get the following error, which sounds quite logical :
错误:在静态成员函数中无效使用成员`parser :: operators'
error: invalid use of member `parser::operators' in static member function
这里是我的问题:如何强制std ::排序使用comp函数,使用来自类的非静态成员的元素?显然,函数应该是非静态的,但如果我不使它静态,我不能使用它...
Here is my question : how can I force std::sort to use a comp function that makes use of elements from non-static members of the class ? Obviously the function should be non-static, but I can't manage to use it if I don't make it static...
先感谢您的帮助,
CFP。
Thanks in advance for your help, CFP.
推荐答案
使用函数代替函数:
struct op_comp : std::binary_function<op_info, op_info, bool>
{
op_comp(parser * p) : _parser(p) {}
bool operator() (const op_info& o1, const op_info& o2) {
return _parser->op_comp(o1, o2);
}
parser * _parser;
};
这样,方法 op_comp
-静态的。然而,调用者需要一个解析器的实例,所有的操作符都存储在其中。这是我们的新函数的用法:
This way the method op_comp
can stay non-static. However the caller needs an instance of the parser, where are all the operators are stored. This is the usage of our new functor:
std::sort(ops.begin(), ops.end(), op_comp(&my_parser));
其中 my_parser
是解析器的实例you正在使用。或者,如果您从解析器调用 std :: sort
,您可以简单地写:
Where my_parser
is the instance of parser you are using. Alternatively, if you are calling std::sort
from the parser, you can simply write:
std::sort(ops.begin(), ops.end(), op_comp(this));
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