需要 STL 排序算法帮助
我在这里使用 std::sort 算法时遇到一些麻烦。 我读到您可以重载小于运算符来对类进行排序，但我收到了各种错误。 我还尝试使用函子，正如您在下面的示例中看到的那样。
我希望有人能看到我在这里做错了什么。
#include <iostream>
#include <vector>
#include <algorithm>
#include <stdlib.h>
#include <time.h>
class Thing {
public:
Thing(int val) {
this->_val = val;
}
bool operator<(Thing& rhs) {
std::cout << "this works!";
return this->val() < rhs.val();
}
int val() {
return this->_val;
}
protected:
int _val;
};
struct Sort {
bool operator()(Thing& start, Thing& end) {
return start.val() < end.val();
}
};
int main (int argc, char * const argv[]) {
std::srand(std::time(NULL));
std::vector<Thing> things;
for(int i = 0; i < 100; i++) {
Thing myThing(std::rand());
things.push_back(myThing);
}
if(things[1] < things[2]) {
//This works
}
//std::sort(things.begin(), things.end()); //This doesn't
//std::sort(things.begin(), things.end(), Sort()); //Neither does this
for(int i = 0; i < 100; i++) {
std::cout << things.at(i).val() << std::endl;
}
return 0;
}
I'm having some troubles with using the std::sort algorithm here. I was reading that you can just overload the less than operator to sort classes, but I have been getting all sorts of errors. I have also tried using a functor as you can see in the example I made below.
I was hoping somebody could see what I'm doing wrong here.
#include <iostream>
#include <vector>
#include <algorithm>
#include <stdlib.h>
#include <time.h>
class Thing {
public:
Thing(int val) {
this->_val = val;
}
bool operator<(Thing& rhs) {
std::cout << "this works!";
return this->val() < rhs.val();
}
int val() {
return this->_val;
}
protected:
int _val;
};
struct Sort {
bool operator()(Thing& start, Thing& end) {
return start.val() < end.val();
}
};
int main (int argc, char * const argv[]) {
std::srand(std::time(NULL));
std::vector<Thing> things;
for(int i = 0; i < 100; i++) {
Thing myThing(std::rand());
things.push_back(myThing);
}
if(things[1] < things[2]) {
//This works
}
//std::sort(things.begin(), things.end()); //This doesn't
//std::sort(things.begin(), things.end(), Sort()); //Neither does this
for(int i = 0; i < 100; i++) {
std::cout << things.at(i).val() << std::endl;
}
return 0;
}
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评论（3）
创建您的
val()和operator<()const函数。Sort::operator()也是如此 — 采用const Thing&而不是Thing&。Make your
val()andoperator<()constfunctions.The same for
Sort::operator()— takeconst Thing&instead ofThing&.我相信你需要改变
成
IOW
，你的代码需要是常量正确的，并且不能
声称它可以修改它实际上没有（也不需要）的东西。
I believe you need to change
into
and
into
IOW, your code needs to be const-correct and not claim it may modify things it in fact doesn't (nor needs to).
尝试使运算符< 通过 const 引用获取其参数。 执行此操作时，您需要更改其实现以直接访问 _val 或（最好）将 val() 设置为 const（因为 const 成员函数无法调用非常量成员函数）。
Try making operator< take its argument by const reference. You'll need to change its implementation to directly access _val or (preferably) make val() const as well when you do this (because a const member function can't call a non-const one).