c++中gbk转utf8时，如果汉字数量为奇数时，最后一个汉字会出现乱码的情况。
原因：
char *strOut = new char[nLength+1]; 申请的长度是不够的，如上面“天安门”是3个汉字，nLength为3。但UTF-8格式一个汉字是占三个字符，至少申请10位(3*3+1)。2、奇数个汉字转码后，再由UTF-8转成GBK时，最后一个字符一直显示为“？”。因为一个汉字转成UTF-8是需要3个字节，3个汉字就成了9个字节，而它会2个字节2个字节地转换成字符，当字节是奇数时最后1个字节转字符就会计算错误，然后直接赋予最后这个字符为“?”，这样改变了数据，影响后面的解码。
解决方案与示例：
#include "stdafx.h"#include <stdio.h>#include <windows.h>#include <sstream>#include <fstream>#include <stdio.h>#include <iostream>//GBK编码转换到UTF8编码using namespace std;int GBKToUTF8(unsigned char * lpGBKStr, unsigned char * lpUTF8Str, int nUTF8StrLen){wchar_t * lpUnicodeStr = NULL;int nRetLen = 0;if (!lpGBKStr) //如果GBK字符串为NULL则出错退出return 0;nRetLen = ::MultiByteToWideChar(CP_ACP, 0, (char *)lpGBKStr, -1, NULL, NULL); //获取转换到Unicode编码后所需要的字符空间长度lpUnicodeStr = new WCHAR[nRetLen + 1]; //为Unicode字符串空间nRetLen = ::MultiByteToWideChar(CP_ACP, 0, (char *)lpGBKStr, -1, lpUnicodeStr, nRetLen); //转换到Unicode编码if (!nRetLen) //转换失败则出错退出return 0;nRetLen = ::WideCharToMultiByte(CP_UTF8, 0, lpUnicodeStr, -1, NULL, 0, NULL, NULL); //获取转换到UTF8编码后所需要的字符空间长度if (!lpUTF8Str) //输出缓冲区为空则返回转换后需要的空间大小{if (lpUnicodeStr)delete[]lpUnicodeStr;return nRetLen;}if (nUTF8StrLen < nRetLen) //如果输出缓冲区长度不够则退出{if (lpUnicodeStr)delete[]lpUnicodeStr;return 0;}nRetLen = ::WideCharToMultiByte(CP_UTF8, 0, lpUnicodeStr, -1, (char *)lpUTF8Str, nUTF8StrLen, NULL, NULL); //转换到UTF8编码if (lpUnicodeStr)delete[]lpUnicodeStr;return nRetLen;}// UTF8编码转换到GBK编码int UTF8ToGBK(unsigned char * lpUTF8Str, unsigned char * lpGBKStr, int nGBKStrLen){wchar_t * lpUnicodeStr = NULL;int nRetLen = 0;if (!lpUTF8Str) //如果UTF8字符串为NULL则出错退出return 0;nRetLen = ::MultiByteToWideChar(CP_UTF8, 0, (char *)lpUTF8Str, -1, NULL, NULL); //获取转换到Unicode编码后所需要的字符空间长度lpUnicodeStr = new WCHAR[nRetLen + 1]; //为Unicode字符串空间nRetLen = ::MultiByteToWideChar(CP_UTF8, 0, (char *)lpUTF8Str, -1, lpUnicodeStr, nRetLen); //转换到Unicode编码if (!nRetLen) //转换失败则出错退出return 0;nRetLen = ::WideCharToMultiByte(CP_ACP, 0, lpUnicodeStr, -1, NULL, NULL, NULL, NULL); //获取转换到GBK编码后所需要的字符空间长度if (!lpGBKStr) //输出缓冲区为空则返回转换后需要的空间大小{if (lpUnicodeStr)delete[]lpUnicodeStr;return nRetLen;}if (nGBKStrLen < nRetLen) //如果输出缓冲区长度不够则退出{if (lpUnicodeStr)delete[]lpUnicodeStr;return 0;}nRetLen = ::WideCharToMultiByte(CP_ACP, 0, lpUnicodeStr, -1, (char *)lpGBKStr, nRetLen, NULL, NULL); //转换到GBK编码if (lpUnicodeStr)delete[]lpUnicodeStr;return nRetLen;}//使用这两个函数的例子int main(){char cGBKStr[] = "奇数个汉字";char * lpGBKStr = NULL;char * lpUTF8Str = NULL;FILE * fp = NULL;int nRetLen = 0;nRetLen = GBKToUTF8((unsigned char *)cGBKStr, NULL, NULL);printf("转换后的字符串需要的空间长度为：%d ", nRetLen);lpUTF8Str = new char[nRetLen + 1];nRetLen = GBKToUTF8((unsigned char *)cGBKStr, (unsigned char *)lpUTF8Str, nRetLen);if (nRetLen){printf("GBKToUTF8转换成功！");}else{printf("GBKToUTF8转换失败！");if (lpGBKStr)delete[]lpGBKStr;if (lpUTF8Str)delete[]lpUTF8Str;return 0;}ofstream out("result.txt");if (out.is_open()){out << lpUTF8Str;out.close();}nRetLen = UTF8ToGBK((unsigned char *)lpUTF8Str, NULL, NULL); //再转回来printf("转换后的字符串需要的空间长度为：%d ", nRetLen);lpGBKStr = new char[nRetLen + 1];nRetLen = UTF8ToGBK((unsigned char *)lpUTF8Str, (unsigned char *)lpGBKStr, nRetLen);if (nRetLen){printf("UTF8ToGBK转换成功！ ");}else{printf("UTF8ToGBK转换失败！ ");if (lpGBKStr)delete[]lpGBKStr;if (lpUTF8Str)delete[]lpUTF8Str;return 0;}ofstream out1("result.txt");if (out1.is_open()){out1 << lpGBKStr;out1.close();}if (lpGBKStr)delete[]lpGBKStr;if (lpUTF8Str)delete[]lpUTF8Str;return 0;}
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