Android之NDK编码转(UTF8->GBK)

基于NDK下的编码转换，当然是直接调用C/C++下的实现效率更高，下面介绍2种方案（不建议通过JNI调用JAVA的实现，尽管这样也能实现编码的转换）。

1. 采用Android系统自带的libicuuc.so库,此库的源代码在/home/george/source/rk3168_v4.2/external/icu4c/common下

2. 采用第三方编码转换库libiconv，源码链接：http://ftp.gnu.org/pub/gnu/libiconv/
libiconv的使用有3个函数:
a) iconv_t iconv_open (const char* tocode, const char* fromcode);
b) size_t iconv (iconv_t cd, const char* * inbuf , size_t * inbytesleft, char* * outbuf , size_t * outbytesleft);
inbytesleft：inbuf的字符串长度；
outbytesleft：输入为outbuf所指向的缓冲区长度，输出为剩余没用到的缓冲区长度；因此转换后的字符串长度为(outbuflen - outbytesleft)；
inbuf, outbuf：返回时指针都后移了，需要注意。
c) int iconv_close (iconv_t cd);

这里采用Android系统自带的库进行编码转换，当然也可采用第三方支持。以下贴出代码段

（gbk和Unicode的互转因为没有用到，所以未贴出，但我想你应该要会了吧）：

#include "libcnv.h"
/* use dl API include file */
#include <dlfcn.h>

/* typedef a function pointer to pointer ucnv_convert method */
/*
see the source code define
int32_t ucnv_convert(const char *toConverterName, const char *fromConverterName,
     char *target, int32_t targetSize,
     const char *source, int32_t sourceSize,
     int32_t * err)
*/
typedef int32_t (*TUCNVCONVERT)(const char *lpcOutEcd, const char *lpcInEcd,
  char* lpOutBuf, int32_t nOutBufLen,
  const char* lpcInStr, int32_t nInStrLen,
  int32_t *pnErrCode);

/* pointer libicuuc.so dl lib */
static void* g_lpdlIcuuc = 0;
/* ucnv_convert method pointer */
static TUCNVCONVERT g_lpfnUcnvConvert = 0;

//在libicuuc.so中找到函数ucnv_convert
int dl_icuuc_init()
{
 g_lpfnUcnvConvert = 0;
 g_lpdlIcuuc = dlopen("/system/lib/libicuuc.so", RTLD_LAZY);
 if (g_lpdlIcuuc != 0)
 {
  int i, j;
  char szDLFnName[32]={0};
  i = 3;
  j = 8;
  //android2.1, ucnv_convert_3_8
  //android2.2, ucnv_convert_4_2
  //android2.3, ucnv_convert_44
  //android4.0, ucnv_convert_46

  //android4.0, ucnv_convert_46

  //android4.1, ucnv_convert_47

  //android4.2, ucnv_convert_48

  //android4.3, ucnv_convert_50

  //android4.4, ucnv_convert_51

  //其尾椎在，在源码的common/unicode/uvernum.h:77:  #define U_ICU_VERSION_SUFFIX _48

  g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, "ucnv_convert_3_8");
  while (0 == g_lpfnUcnvConvert)
  {
   memset(szDLFnName, 0, 32*sizeof(char));
   sprintf(szDLFnName, "ucnv_convert_%d%d", i, j);
   g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, szDLFnName);
   if (g_lpfnUcnvConvert != 0){
    return 1;
   }
   sprintf(szDLFnName, "ucnv_convert_%d_%d", i, j);
   g_lpfnUcnvConvert = (TUCNVCONVERT)dlsym(g_lpdlIcuuc, szDLFnName);
   if (g_lpfnUcnvConvert != 0){
    return 1;
   }
   j++;
   if (j > 9){
    j = 1;
    i++;
    if (i > 5){
     break;
    }
   }
  }
 }
 return 0;
}
int dl_icuuc_uninit()
{
 if (g_lpdlIcuuc != 0)
 {
  dlclose(g_lpdlIcuuc);
  g_lpdlIcuuc = 0;
 }
 return 1;
}
//utf-8,gb2312,ucs4
//utf-8:  一个英文字母或者是数字占用一个字节，汉字占3个字节
//gb2312: 一个英文字母或者是数字占用一个字节，汉字占2个字节
int32_t dl_icuuc_gbk2utf8(char *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
 int32_t iret;
 iret = 0;
 if (outbuf != 0 && instring != 0)
 {
  if (g_lpfnUcnvConvert != 0)
  {
   int32_t err_code = 0;
   iret = g_lpfnUcnvConvert("utf-8", "gb2312"
      ,outbuf, buflen
      ,instring, inlen
      ,&err_code);
  }
 }
 return iret;
}
int32_t dl_icuuc_utf82gbk(char *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
 int32_t iret;
 iret = 0;
 if (outbuf != 0 && instring != 0)
 {
  if (g_lpfnUcnvConvert != 0)
  {
   int32_t err_code = 0;
   iret = g_lpfnUcnvConvert("gb2312", "utf-8"
      ,outbuf, buflen
      ,instring, inlen
      ,&err_code);
  }
 }
 return iret;
}
int32_t dl_icuuc_unicode2utf8(char *outbuf, int32_t buflen, const unsigned short *instring, int32_t inlen)
{
 int32_t iret;
 iret = 0;
 if (outbuf != 0 && instring != 0)
 {
  if (g_lpfnUcnvConvert != 0)
  {
   int32_t err_code = 0;
   iret = g_lpfnUcnvConvert("utf-8", "ucs4"
      ,outbuf, buflen
      ,(const char *)instring, inlen*sizeof(unsigned short)/sizeof(char)
      ,&err_code);
  }
 }
 return iret;
}
int32_t dl_icuuc_utf82unicode(unsigned short *outbuf, int32_t buflen, const char *instring, int32_t inlen)
{
 int32_t iret;
 iret = 0;
 if (outbuf != 0 && instring != 0)
 {
  if (g_lpfnUcnvConvert != 0)
  {
   int32_t err_code = 0;
   iret = g_lpfnUcnvConvert("ucs4", "utf-8"
      ,(char *)outbuf, buflen*sizeof(unsigned short)/sizeof(char)
      ,instring, inlen
      ,&err_code);
  }
 }
 return iret;
}