Question

我想写一个像“bind1st，bind2nd”这样的函数来支持使用stl sort排序的多字段。 无法使用std：bind，因为我的g ++版本是3.4.5

它被称为：

#include <alogritm>
std::sort(begin(), end(), bind3rd(SortCond(), indicate));

我的模板功能是：

#ifndef  __INCLUDE_TRIPLE_FUNCTION_H_
#define  __INCLUDE_TRIPLE_FUNCTION_H_

#define TRIPLE_ARG(Operation, Type) Operation::Type
// Define the triple_function prototype
template<class Arg1, class Arg2, class Arg3, class Result>
struct triple_function
{
    // Define the argument type alias
    typedef Arg1 first_argument_type;
    typedef Arg2 second_argument_type;
    typedef Arg3 third_argument_type;
    typedef Result result_type;
};

template <class Operation>
class binder3rd : public binary_function<typename TRIPLE_ARG(Operation, first_argument_type),
    typename TRIPLE_ARG(Operation, second_argument_type), typename TRIPLE_ARG(Operation, result_type)>
{
protected:
    Operation m_op;
    typename Operation::third_argument_type value;
public:
    binder3rd(const Operation& x, const typename Operation::third_argument_type y):m_op(x), value(y){}

    // Convert this function to binary_function using the third argment
    typename Operation::result_type operator()(const typename Operation::first_argument_type& x, const typename Operation::second_argument_type& y) const
    {
        return m_op(x, y, value);
    }

};

// bind3rd function implementation
template<class Operation, class Arg>
inline binder3rd<Operation> bind3rd(const Operation& fn, const Arg& x)
{
    return binder3rd<Operation>(fn, x);
}

#endif  //__INCLUDE/TRIPLE_FUNCTION_H_
/* vim: set expandtab ts=4 sw=4 sts=4 tw=100: */

我的测试cpp文件是：

#include <algorithm>
#include <cstdlib>

#include "triple_function.h"

using namespace std;

class TestClass{
public:
    int arr[16];

    TestClass() {
        for (int i = 0; i < 16; ++i) {
            arr[i] = rand() % 100;
        }
    }
};

// sort by which fields
class Indicate {
public:
    int ind[16];
};


struct SortA : public triple_function < TestClass, TestClass, const Indicate, bool > 
{
    bool operator () (const TestClass& a, const TestClass& b, 
            const Indicate& indicate) const 
    {
        for (int i = 0; i < 16; ++i) {
            int pos = indicate.ind[i];
            if (a.arr[pos] == b.arr[pos]) {
                continue ;
            }
            return a.arr[pos] < b.arr[pos];
        }
        return false;
    }
};


int main() {
    TestClass a[10];

    Indicate ind;
    for(int i = 0; i < 16; ++i) {
        ind.ind[i] = i;
    }

    sort(a, a+10, bind3rd(SortA(), ind));
    // bind3rd(SortA, ind);
}

使用g ++编译时，我得到了这些编译错误：我的代码出了什么问题？

In file included from test.cpp:19:
triple_function.h:32: error: expected template-name before '<' token
triple_function.h:32: error: expected `{' before '<' token
triple_function.h:32: error: expected unqualified-id before '<' token
test.cpp: In function `int main()':
test.cpp:62: error: invalid use of undefined type `class binder3rd<SortA>'
triple_function.h:32: error: declaration of `class binder3rd<SortA>'
triple_function.h: In function `binder3rd<Operation> bind3rd(const Operation&, const Arg&) [with Operation = SortA, Arg = Indicate]':
test.cpp:62:   instantiated from here
triple_function.h:52: error: return type `class binder3rd<SortA>' is incomplete
triple_function.h:53: error: invalid use of undefined type `class binder3rd<SortA>'
triple_function.h:32: error: declaration of `class binder3rd<SortA>'

Answer 1

使用std::bind，您可以执行以下操作：像这样：

#include <functional>

...

bool my_compare(const TestClass& a, const TestClass& b, 
                const Indicate& indicate)
{
    ...
}

int main()
{
    ...

    using namespace std::placeholders;
    std::sort(a, a+10, std::bind(my_compare, _1, _2, ind));
}

Answer 2

编译器正在绊倒你的binary_function基类。如果您的意思是std::binary_function，那么#include <functional>和std::前缀。当然，既然你实际上并没有定义二元函数，我不确定基类是否合适...

正如其他人所说，如果您可以使用C ++ 11，std::bind是解决此问题的更好方法。

使用自定义“bind3rd”函数时，c ++使用模板编译错误

2 个答案: