你知道如何自定义sort函数中的比较函数

class Solution {
public:
    static bool compare(const string& s1, const string& s2)
    {
        string ab = s1 + s2;
        string ba = s2 + s1;
        return ab < ba; //升序排列。如改为ab > ba, 则为降序排列
    }
    string PrintMinNumber(vector<int> numbers) 
    {
        string result;
        if(numbers.size() <= 0) return result;
        vector<string> num2str;
        for(int i = 0; i < numbers.size(); i++)
        {
            stringstream ss;
            ss << numbers[i];
            string s = ss.str();
            num2str.push_back(s);
        }
        sort(num2str.begin(), num2str.end(), compare);
        for(int i = 0; i < num2str.size(); i++)
        {
            result.append(num2str[i]);
        }
        return result;
    }
};

// sort algorithm example
#include <iOStream>     // std::cout
#include <algorithm>    // std::sort
#include <vector>       // std::vector
bool myfunction (int i,int j) { return (i<j); }
struct myclass {
  bool operator() (int i,int j) { return (i<j);}
} myobject;
int main () {
  int myints[] = {32,71,12,45,26,80,53,33};
  std::vector<int> myvector (myints, myints+8);               // 32 71 12 45 26 80 53 33
  // using default comparison (operator <):
  std::sort (myvector.begin(), myvector.begin()+4);           //(12 32 45 71)26 80 53 33
  // using function as comp
  std::sort (myvector.begin()+4, myvector.end(), myfunction); // 12 32 45 71(26 33 53 80)
  // using object as comp
  std::sort (myvector.begin(), myvector.end(), myobject);     //(12 26 32 33 45 53 71 80)
  // print out content:
  std::cout << "myvector contains:";
  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';
  return 0;
}

    static bool compare(const string& s1, const string& s2)
    {
        string ab = s1 + s2;
        string ba = s2 + s1;
        return ab < ba; //升序排列。如改为ab > ba, 则为降序排列
    }

bool cmp(int a,int b)
{
return a>b;
}

struct node{
int a;
int b;
double c;
}

bool cmp(node x,node y)
{
if(x.a!=y.a) return x.a
if(x.b!=y.b) return x.b>y.b;
return return x.c>y.c;
} 

qsort(s[0],n,sizeof(s[0]),cmp);
int cmp(const void *a,const void *b)
{
return *(int *)a-*(int *)b;
}

int num[100];
Sample:
int cmp ( const void *a , const void *b )
{
return *(int *)a - *(int *)b;
}
qsort(num,100,sizeof(num[0]),cmp);

char Word[100];
Sample:
int cmp( const void *a , const void *b )
{
return *(char *)a - *(int *)b;
}
qsort(word,100,sizeof(word[0]),cmp);

double in[100];
int cmp( const void *a , const void *b )
{
return *(double *)a > *(double *)b ? 1 : -1;
}
qsort(in,100,sizeof(in[0]),cmp)；

struct In
{
double data;
int other;
}s[100]
//按照data的值从小到大将结构体排序,关于结构体内的排序关键数据data的类型可以很多种，参考上面的例子写
int cmp( const void *a ,const void *b)
{
return ((In *)a)->data - ((In *)b)->data ;
}
qsort(s,100,sizeof(s[0]),cmp);

struct In
{
int x;
int y;
}s[100];
//按照x从小到大排序，当x相等时按照y从大到小排序
int cmp( const void *a , const void *b )
{
struct In *c = (In *)a;
struct In *d = (In *)b;
if(c->x != d->x) return c->x - d->x;
else return d->y - c->y;
}
qsort(s,100,sizeof(s[0]),cmp);

struct In
{
int data;
char str[100];
}s[100];
//按照结构体中字符串str的字典顺序排序
int cmp ( const void *a , const void *b )
{
return strcmp( ((In *)a)->str , ((In *)b)->str );
}
qsort(s,100,sizeof(s[0]),cmp);

int cmp(const void *a,const void *b) //重点cmp函数，把除了1点外的所有点，旋转角度排序
{
struct point *c=(point *)a;
struct point *d=(point *)b;
if( calc(*c,*d,p[1]) < 0) return 1;
else if( !calc(*c,*d,p[1]) && dis(c->x,c->y,p[1].x,p[1].y) < dis(d->x,d->y,p[1].x,p[1].y)) //如果在一条直线上，则把远的放在前面
return 1;
else return -1;
}