c++ :parse utf-8 file failed using expat library

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C++

UTF-8

I have a strange problem when I parse utf-8 file using expat. The code can parse xml correctly in windows.(I test this usign vc6.0), But it cannot parse xml when i run the code in android. I don't know why, the code and the xml file is the same.
For solving this problem, i did some tests:
1. change xml file 's encoding is ANSI: if file doesn't contain chinese, it can be parsed correctly; if not ,parse failed.
2. change xml file's encoding is UTF-8: whatever,the code cannot parse it.

the following is my code :

#include <fstream>
#include <string>
#include <stdlib.h>
#include <stdio.h>
#include <algorithm>
#include "expat.h"
using namespace std;

bool  LoadXmlFile(string strfilename);

int Depth;
ize_t offs;
int overflow;

// if the element is the one we're after, convert the character data to
// an integer value
static void 
startElement(void *userData, const char *name, const char **atts)
{
  puts(name);
  int *depthPtr = (int *)userData;
  *depthPtr += 1;
}

static void 
endElement(void *userData, const char *name)
{
  puts(name);
  int *depthPtr = (int *)userData;
  *depthPtr -= 1;
  }

bool  LoadXmlFile(string strfilename)
{    
    XML_Parser parser=XML_ParserCreate(NULL);
    if(!parser)
    {
        printf("Create XML praser FAIL\n");
		return false;
    }
    printf("Enter LoadXmlFile\n");	
    m_strxmlFileName = strfilename;
    long size=0;
    FILE* xmlFile=fopen(m_strxmlFileName.c_str(),"rt");
    if(NULL==xmlFile)
    {
        printf("loding file failed\n")
        return false;
    }
    char buf[100];
    int done=0;
    XML_SetUserData(parser, &Depth);
    XML_SetElementHandler(parser, startElement, endElement); 
    XML_SetCharacterDataHandler(parser,CharHandler);

    //reading xml file 
    do
    {
	memset(buf, 0, sizeof(char) * 100);
        int len = (int)fread(buf, 1,sizeof(buf), xmlFile);
        done = len < sizeof(buf);
        printf("buf first chars :%s\n",buf);
        if(!XML_Parse(parser, buf, len, done))
        {
            done=1;
            printf("Parse requestconfig xml FAILED\n");
            fclose(xmlFile);
            return false;
        }
    }while(!done);

    fclose(xmlFile);
} 

int main ()
{
  if(!LoadXmlFile("requestconfig.xml"))
      printf("parse xml failed");    
}

the xml that i use to test is :

<clientrequest requestid="20" desc="中国">
</clientrequest>

thank you very much.