c++ - rapidxml 在 wchar_t 内容上抛出异常

Question

在win32平台解析wchar_t内容时，rapidxml可能会抛出parse_error异常。内容:

<xml att='最好' />

这是我的测试代码:

/*
 *  @file  : TestRapidXmlBug.cpp
 *  @author: shilyx
 *  @date  : 2015-09-16 11:02:22.886
 *  @note  : Generated by SlxTemplates
 */

#include <Windows.h>
#include "rapidxml.hpp"
#include <iostream>
#include <string>

using namespace std;
using namespace rapidxml;

int main(int argc, char *argv[])
{
    // data block
    unsigned char szData[] = {
        0x3C, 0x00, 0x78, 0x00, 0x6D, 0x00, 0x6C, 0x00, 0x20, 0x00, 0x61, 0x00, 0x74, 0x00, 0x74, 0x00, 0x3D, 
        0x00, 0x27, 0x00, 0x00, 0x67, 0x7D, 0x59, 0x27, 0x00, 0x20, 0x00, 0x2F, 0x00, 0x3E, 0x00, 0x00, 0x00};

    // uft8 string
    char szDataUtf8[sizeof(szData) * 10] = "";

    // ucs2 string
    wchar_t *szDataUcs2 = (wchar_t *)szData;

    WideCharToMultiByte(CP_UTF8, 0, szDataUcs2, -1, szDataUtf8, sizeof(szDataUtf8), NULL, NULL);

    try
    {
        xml_document<wchar_t> xml;

        cout<<"-------------------------wchar_t"<<endl;
        xml.parse<0>(szDataUcs2);  // will throw parse_error
        cout<<"success"<<endl;
    }
    catch (parse_error &ex)
    {
        cout<<"exception: "<<ex.what()<<endl;
        cout<<"failled"<<endl;
    }

    try
    {
        xml_document<char> xml;

        cout<<"-------------------------char"<<endl;
        xml.parse<0>(szDataUtf8);  // will not throw any exception
        cout<<"success"<<endl;
    }
    catch (parse_error &ex)
    {
        cout<<ex.what()<<endl;
        cout<<"failled"<<endl;
    }

    return 0;
}

它将在以下位置抛出异常:

        // Make sure that end quote is present
        if (*text != quote)
            RAPIDXML_PARSE_ERROR("expected ' or \"", text);
        ++text;     // Skip quote

原因可能是:

// Skip characters until predicate evaluates to true
template<class StopPred, int Flags>
static void skip(Ch *&text)
{
    Ch *tmp = text;
    while (StopPred::test(*tmp))
        ++tmp;
    text = tmp;
}

StopPred::test 函数:

// Detect attribute value character
template<Ch Quote>
struct attribute_value_pure_pred
{
    static unsigned char test(Ch ch)
    {
        if (Quote == Ch('\''))
            return internal::lookup_tables<0>::lookup_attribute_data_1_pure[static_cast<unsigned char>(ch)];
        if (Quote == Ch('\"'))
            return internal::lookup_tables<0>::lookup_attribute_data_2_pure[static_cast<unsigned char>(ch)];
        return 0;       // Should never be executed, to avoid warnings on Comeau
    }
};

static_cast 将 wchar_t(0x6700) 更改为 unsigned char(0x00)，跳过操作停止。

---

这是一个错误吗？或者将 rapidxml 与 wchar_t 一起使用是错误的？rapidxml的最后更新日期是2013-04-26，我觉得应该够稳定了。

Answer 1

Rapidxml 不完全支持 UTF-16、UTF-32 或其他宽编码。

Current version does not fully support UTF-16 or UTF-32, so use of wide characters is somewhat incapacitated. However, it should succesfully parse wchar_t strings containing UTF-16 or UTF-32 if endianness of the data matches that of the machine.

如您所见，一个有趣的巧合是字符 0x6700 在转换为用于 rapidxml 内部表查找的 unsigned char 时是 0 , 这不是有效的属性字符，因此终止解析。我想文档应该阐明对宽编码的部分支持是可用的，但要注意不要使用 Basic Latin 和 Latin-1 之外的代码点(即 U+0000 ~ U+00FF)。

解决方案是改用 UTF-8。