http://blog.csdn.net/fengrx/article/details/4330946

#include <windows.h>  
#include <iostream.h>  
#include "Shlwapi.h"  
void main(void) 
{ 
    char szOut[MAX_PATH] = ""; 
    char szFrom[ ] = "c://a//b//path"; 
    char szTo[ ] = "c://a//x//y//file"; 
    cout  <<  "The relative path is relative from: "; 
    cout  <<  szFrom; 
    cout  <<  "/n"; 
    cout  <<  "The relative path is relative to: "; 
    cout  <<  szTo; 
    cout  <<  "/n"; 
    PathRelativePathTo(szOut, 
                       szFrom, 
                       FILE_ATTRIBUTE_DIRECTORY, 
                       szTo, 
                       FILE_ATTRIBUTE_NORMAL); 
    cout  <<  "The relative path is: "; 
    cout  <<  szOut; 
    cout  <<  "/n"; 
} 
#include <windows.h>
#include <iostream.h>
#include "Shlwapi.h"
void main(void)
{
    char szOut[MAX_PATH] = "";
    char szFrom[ ] = "c://a//b//path";
    char szTo[ ] = "c://a//x//y//file";
    cout  <<  "The relative path is relative from: ";
    cout  <<  szFrom;
    cout  <<  "/n";
    cout  <<  "The relative path is relative to: ";
    cout  <<  szTo;
    cout  <<  "/n";
    PathRelativePathTo(szOut,
                       szFrom,
                       FILE_ATTRIBUTE_DIRECTORY,
                       szTo,
                       FILE_ATTRIBUTE_NORMAL);
    cout  <<  "The relative path is: ";
    cout  <<  szOut;
    cout  <<  "/n";
}

OUTPUT:
==================
The relative path is relative from: c:/a/b/path
The relative path is relative to: c:/a/x/y/file
The relative path is: ../../x/y/file