c++ - 如何在类中使用 "void sort(_RAIter, _RAIter, _Compare)"头文件的 "algorithm"

Question

我正在编写代码，但无法在类中使用 sort() 方法。

class MyClass {
    struct MyStruct {
        ...
    } MyStructArr[10];

    void fun() {
        ...  // setting values of MyStructArr
        sort(MyStructArr, MyStructArr + 10, cmp);     // !ERROR!
    }

    int cmp(struct MyStruct a, struct MyStruct b) {
        ...
    }
};

但是相同的代码在没有类的情况下也能工作

struct MyStruct {
   ...
} MyStructArr[10];

int main() {
    ...  // setting values of MyStructArr
    sort(MyStructArr, MyStructArr + 10, cmp); 
    return 0;
}

int cmp(struct MyStruct a, struct MyStruct b) {
    ...
}

我无法理解为什么带有比较功能的 sort(...) 在内部不起作用类。
这是错误:

SuffixArray.cpp: In member function 'void SuffixArray_Entry::suffixArray()':
SuffixArray.cpp:31:43: error: no matching function for call to 'sort(SuffixArray_Entry::SuffixArray_entry [65536], SuffixArray_Entry::SuffixArray_entry*, <unresolved overloaded function type>)'
             sort(L, L + N, SuffixArray_cmp);
                                           ^
SuffixArray.cpp:31:43: note: candidates are:
In file included from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62:0,
                 from SuffixArray.cpp:3:
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:5461:5: note: template<class _RAIter> void std::sort(_RAIter, _RAIter)
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
     ^
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:5461:5: note:   template argument deduction/substitution failed:
SuffixArray.cpp:31:43: note:   candidate expects 2 arguments, 3 provided
             sort(L, L + N, SuffixArray_cmp);
                                           ^
In file included from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62:0,
                 from SuffixArray.cpp:3:
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:5497:5: note: void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = SuffixArray_Entry::SuffixArray_entry*; _Compare = int (SuffixArray_Entry::*)(SuffixArray_Entry::SuffixArray_entry, SuffixArray_Entry::SuffixArray_entry)]
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
     ^
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:5497:5: note:   no known conversion for argument 3 from '<unresolved overloaded function type>' to 'int (SuffixArray_Entry::*)(SuffixArray_Entry::SuffixArray_entry, SuffixArray_Entry::SuffixArray_entry)'
make.exe[2]: *** [build/Debug/MinGW-Windows/SuffixArray.o] Error 1
make.exe[2]: Leaving directory `/c/Users/Afzalex/Documents/NetBeansProjects/TestingStore/CPPStoreRoom'
make.exe[1]: *** [.build-conf] Error 2
make.exe[1]: Leaving directory `/c/Users/Afzalex/Documents/NetBeansProjects/TestingStore/CPPStoreRoom'
make.exe": *** [.build-impl] Error 2

这是我原始程序的错误堆栈跟踪。我将 Netbeans 与 MinGW 结合使用

Answer 1

声明成员函数cmp作为静态成员函数。考虑到如果函数的参数是引用会好得多。

另一种方法是在类内部定义一个功能对象。例如

class MyClass {
    struct MyStruct {
        ...
    } MyStructArr[10];

    struct cmp
    {
        bool operator ()( const struct MyStruct &a, const struct MyStruct &b ) const
        {
            //....
        }
    };

    void fun() {
        ...  // setting values of MyStructArr
        sort(MyStructArr, MyStructArr + 10, cmp());
    }

        ...

你也可以定义operator <用于结构 MyStruct .在这种情况下，您可以调用 std::sort没有谓词。