C++_归并排序（纯C版）

#include <iostream>
#include <stdlib.h>

using namespace std;
int compared(const void *key1,const void *key2)
{
	//cout<<"enter compare"<<endl;
	const int* iKey1 = (int*)key1;
	const int* iKey2 = (int*)key2;
	//cout<<*iKey1<<endl;
	//cout<<*iKey2<<endl;

	if(*iKey1>*iKey2){
		//cout<<"big"<<endl;
		return 1;
	}
	else if(*iKey1==*iKey2){
		//cout<<"equal"<<endl;
		return 0;
	}
	else if(*iKey1<*iKey2)
	{
		//cout<<"less"<<endl;
		return -1;
	}
}

//k设置为size-1
//i设置为0
//j设置为中间数
static int merge(void* data, int esize, int i, int j, int k, int (*compare)
(const void* key1,const void* key2))
{
    char *a = (char*)data, *m=NULL;
    int ipos, jpos, mpos;

    ipos = i;
    jpos = j+1;
    mpos = 0;
    
    if((m=(char*)malloc(esize*((k-i)+1)))==NULL )
	{
		return -1;	
	}
    
	while(ipos<=j||jpos<=k)
	{
		if(ipos>j)
		{
		//the left elements has no more elements to merge
			while(jpos<=k)
			{
				memcpy(&m[mpos*esize],&a[jpos*esize],esize);
				jpos++;
				mpos++;
			}
			continue;
		}
		else if(jpos>k)
		{
			//right division has no more elements to merge.
			while(ipos<=j)
			{
				memcpy(&m[mpos*esize],&a[ipos*esize],esize);
				ipos++;
				mpos++;
			}
			continue;
		}
		if(compare(&a[ipos*esize],&a[jpos*esize])<0)
		{
			memcpy(&m[mpos*esize],&a[ipos*esize],esize);
			ipos++;
			mpos++;
		}
		else
		{
			memcpy(&m[mpos*esize],&a[jpos*esize],esize);
			jpos++;
			mpos++;
		}
	}
	//prepare to merge data
	memcpy(&a[i*esize], m,esize*((k-1)+1));

	free(m);

	return 0;
    
}    

int mgsort(void *data, int size, int esize, int i,int k,int (*compare)
(const void* key1,const void* key2))
{
	int j;
	//stop the recursion when no more element divisions can be made.
	if(i<k)
	{
		//determine where to divide the elements
		j = (int)(((i+k-1))/2);

		if(mgsort(data,size,esize,i,j,compared)<0)
		{
			return -1;
		}
		if(mgsort(data,size,esize,j+1,k,compared)<0)
		{
			return -1;
		}
		//merge the two sorted divisions into a single sorted set
		if(merge(data,esize,i,j,k,compared)<0)
		{
			return -1;
		}
	}
		return 0;
}


int main(int argc, char *argv[])
{
	int a[]={4,2,5,8,4,6};

	for(int i=0;i<6;i++)
	{
		cout<<a[i]<<",";
	}
	cout<<endl;

	mgsort(a,6,4,0,5,compared);

	for(int i=0;i<6;i++)
	{
		cout<<a[i]<<",";
	}
	cout<<endl;
  system("PAUSE");	
  return 0;
}