C++判断文本编码

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;

enum TEXT_TYPE
{
    TEXT_ANSI = 0,
    TEXT_UTF8 = 1,
    TEXT_UTF8_BOM = 2,
    TEXT_UTF16_LE = 3,
    TEXT_UTF16_BE = 4,
    TEXT_UNKNOW = 5,
};

//检查是否为无BOM的UTF8
bool check_utf8_without_bom(const string &file_name)
{
    ifstream file_in;
    file_in.open(file_name, ios::in);

    if (!file_in.is_open())
    {
        cout << "打开文件失败" << endl;
        return false;
    }

    stringstream buffer;
    buffer << file_in.rdbuf();
    file_in.close();
    string text = buffer.str();

    size_t len = text.size();
    int n = 0;
    unsigned char ch;
    bool b_all_ascii = true;

    //0x00-0x7F为ASCII码范围

    for (size_t i = 0; i < len; ++i)
    {
        ch = text[i];

        if ((ch & 0x80) != 0)
        {
            b_all_ascii = false;
        }

        if (n == 0)
        {
            if (ch >= 0x80)
            {
                if (ch >= 0xFC && ch <= 0xFD)
                {
                    n = 6;
                }
                else if (ch >= 0xF8)
                {
                    n = 5;
                }
                else if (ch >= 0xF0)
                {
                    n = 4;
                }
                else if (ch >= 0xE0)
                {
                    n = 3;
                }
                else if (ch >= 0xC0)
                {
                    n = 2;
                }
                else
                {
                    return false;
                }
                n--;
            }
        }
        else
        {
            if ((ch & 0xC0) != 0x80)//在UTF-8中，以位模式10开始的所有字节是多字节序列的后续字节
            {
                return false;
            }
            n--;
        }
    }

    if (n > 0)
    {
        return false;
    }

    if (b_all_ascii)
    {
        return false;
    }

    return true;
}

//检查文本编码
TEXT_TYPE check_text_encode(const string &file_name)
{
    /*
    ANSI                     无格式定义                        对于中文编码格式是GB2312;
    Unicode little endian    文本里前两个字节为FF FE           字节流是little endian
    Unicode big endian       文本里前两个字节为FE FF           字节流是big endian
    UTF-8带BOM               前两字节为EF BB，第三字节为BF     带BOM
    UTF-8不带BOM             无格式定义,需另加判断               不带BOM
    */

    ifstream file_in(file_name, ios::binary);
    if (!file_in.is_open())
    {
        cout << "打开文件失败" << endl;;
        return TEXT_UNKNOW;
    }

    int head;
    unsigned char ch;
    file_in.read((char*)&ch, sizeof(ch));
    head = ch << 8;
    file_in.read((char*)&ch, sizeof(ch));
    head |= ch;

    file_in.close();
    TEXT_TYPE result_code;
    switch (head)
    {
    case 0xFFFE:
        result_code = TEXT_UTF16_LE;
        break;
    case 0xFEFF:
        result_code = TEXT_UTF16_BE;
        break;
    case 0xEFBB:
        result_code = TEXT_UTF8_BOM;
        break;
    default:
        if (check_utf8_without_bom(file_name))
            result_code = TEXT_UTF8;
        else
            result_code = TEXT_ANSI;
        break;
    }
    return result_code;
}

int main(int argc, char* argv[])
{
    string str1 = "E:\\Book\\ANSI.txt";
    string str2 = "E:\\Book\\UTF8.txt";
    string str3 = "E:\\Book\\UTF8_BOM.txt";

    TEXT_TYPE txttype1 = check_text_encode(str1);
    TEXT_TYPE txttype2 = check_text_encode(str2);
    TEXT_TYPE txttype3 = check_text_encode(str3);

    getchar();
    return 0;
}

参考链接:

https://www.jb51.net/article/128576.htm

https://www.cnblogs.com/Toya/p/11433441.html