C++实现编码转换的示例代码

代码地址

https://github.com/gongluck/Code-snippet/tree/master/cpp/code%20conversion

需求

编码转换在实际开发中经常遇到，通常是ANSI、Unicode和Utf-8之间相互转换。实现也有很多种，有查表法、使用C++11、使用boost、使用系统API。C++11和boost几乎可以实现一套代码，在linux和windows都能使用，但实际会有很多坑，相当于代码几乎不改，但是要改一下系统环境。所以有一种实现就是判断系统的版本，然后选择不同的系统api进行编码转换。

实现

目前只实现Windows下的编码转换，以后需要在linux下使用编码转换再做补充。windows下的编码转换基本围绕unicode做处理。例如ANSI->UTF-8，就是先将ANSI->unicode，再将unicode->UTF-8。

// convert.h
/*
 * @Author: gongluck
 * @Date: 2020-03-23 16:06:23
 * @Last Modified by: gongluck
 * @Last Modified time: 2020-03-23 16:09:30
 */

// Character encoding conversion

#pragma once

#include <string>

namespace gconvert
{
// ANSI->Unicode
int ansi2uni(const std::string& ansi, std::wstring& uni);

// Unicode->ANSI
int uni2ansi(const std::wstring& uni, std::string& ansi);

// UTF8->Unicode
int utf82uni(const std::string& utf8, std::wstring& uni);

// Unicode->UTF8
int uni2utf8(const std::wstring& uni, std::string& utf8);

// ANSI->UTF8
int ansi2utf8(const std::string& ansi, std::string& utf8);

// UTF8->ANSI
int utf82ansi(const std::string& utf8, std::string& ansi);
} // namespace gconvert

//convert.cpp
/*
 * @Author: gongluck
 * @Date: 2020-03-23 16:13:01
 * @Last Modified by: gongluck
 * @Last Modified time: 2020-03-23 16:34:50
 */

#include "convert.h"

#include <iostream>

#ifdef _WIN32
#include <windows.h>
#endif

namespace gconvert
{
#ifdef _WIN32
  static int multi2uni(const std::string& multi, std::wstring& uni, UINT code)
  {
    auto len = MultiByteToWideChar(code, 0, multi.c_str(), -1, nullptr, 0);
    if (len <= 0)
    {
      std::cerr << __FILE__ << " : " << __LINE__ << " : " << GetLastError() << std::endl;
      return -1;
    }
    WCHAR* buf = new WCHAR[len];
    if (buf == nullptr)
    {
      std::cerr << __FILE__ << " : " << __LINE__ << " : " << "can not new buf, size : " << len << std::endl;
      return -2;
    }
    len = MultiByteToWideChar(code, 0, multi.c_str(), -1, buf, len);
    uni.assign(buf);
    delete[]buf;
    buf = nullptr;
    return len;
  }

  static int uni2multi(const std::wstring& uni, std::string& multi, UINT code)
  {
    auto len = WideCharToMultiByte(code, 0, uni.c_str(), -1, nullptr, 0, nullptr, nullptr);
    if (len <= 0)
    {
      std::cerr << __FILE__ << " : " << __LINE__ << " : " << GetLastError() << std::endl;
      return -1;
    }
    CHAR* buf = new CHAR[len];
    if (buf == nullptr)
    {
      std::cerr << __FILE__ << " : " << __LINE__ << " : " << "can not new buf, size : " << len << std::endl;
      return -2;
    }
    len = WideCharToMultiByte(code, 0, uni.c_str(), -1, buf, len, nullptr, nullptr);
    multi.assign(buf);
    delete[]buf;
    buf = nullptr;
    return len;
  }
#endif

// ANSI->Unicode
int ansi2uni(const std::string& ansi, std::wstring& uni)
{
#ifdef _WIN32
  return multi2uni(ansi, uni, CP_ACP);
#endif
  return 0;
}

// Unicode->ANSI
int uni2ansi(const std::wstring &uni, std::string &ansi)
{
#ifdef _WIN32
  return uni2multi(uni, ansi, CP_ACP);
#endif
  return 0;
}

// UTF8->Unicode
int utf82uni(const std::string& utf8, std::wstring& uni)
{
#ifdef _WIN32
  return multi2uni(utf8, uni, CP_UTF8);
#endif
  return 0;
}

// Unicode->UTF8
int uni2utf8(const std::wstring& uni, std::string& utf8)
{
#ifdef _WIN32
  return uni2multi(uni, utf8, CP_UTF8);
#endif
  return 0;
}

// ANSI->UTF8
int ansi2utf8(const std::string &ansi, std::string &utf8)
{
  std::wstring uni;
  auto len = ansi2uni(ansi, uni);
  if (len <= 0)
  {
    return -3;
  }
  return uni2utf8(uni, utf8);
}

// UTF8->ANSI
int utf82ansi(const std::string &utf8, std::string &ansi)
{
  std::wstring uni;
  auto len = utf82uni(utf8, uni);
  if (len <= 0)
  {
    return -3;
  }
  return uni2ansi(uni, ansi);
}
} // namespace gconvert

//testcode
#include <iostream>

#include "../code conversion/convert.h"

int main()
{
  std::string ansi = "你好，世界！";
  std::wstring uni;
  std::string utf8;
  ret = gconvert::ansi2uni(ansi, uni);
  ret = gconvert::ansi2utf8(ansi, utf8);
  ret = gconvert::uni2ansi(uni, ansi);
  ret = gconvert::uni2utf8(uni, utf8);
  ret = gconvert::utf82ansi(utf8, ansi);
  ret = gconvert::utf82uni(utf8, uni);
  return 0;
}

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