类型转换（wchar_t*/char*互转、TCHAR* /char*互转、string /double互转、long double转string）

1、char*转wchar_t*

wchar_t* toolC::char2wchar(const char* cchar)
{
    wchar_t* m_wchar;
    int len = MultiByteToWideChar(CP_ACP, 0, cchar, strlen(cchar), NULL, 0);
    m_wchar = new wchar_t[len+1];
    MultiByteToWideChar(CP_ACP, 0, cchar, strlen(cchar), m_wchar, len);
    m_wchar[len] = '\0';
    return m_wchar;
}

2、wchar_t*转char*

char* toolC::wchar2char(const wchar_t* wchar)
{
    char* m_char;
    int len = WideCharToMultiByte(CP_ACP, 0, wchar, wcslen(wchar), NULL, 0, NULL, NULL);
    m_char = new char[len+1];
    WideCharToMultiByte(CP_ACP, 0, wchar, wcslen(wchar), m_char, len, NULL, NULL);
    m_char[len] = '\0';
    return m_char;
}

3、TCHAR* 转char*

char* toolC::TCHARToChar(TCHAR* pTchar)
{
    char* pChar = nullptr;
    int len = wcslen(pTchar) + 1;
    pChar= new char[len * 2];
    WideCharToMultiByte(CP_ACP, 0, pTchar, len, pChar, 2 * len, NULL, NULL);
    return pChar;
}

 4、char* 转TCHAR

TCHAR* toolC::TCHARToChar(char* pChar)
{
    TCHAR* pTchar = nullptr;
    int len = strlen(pChar) + 1;
    pTchar= new wchar_t[len];
    MultiByteToWideChar(CP_ACP, 0, pChar, len, pTchar, len);
    return pTchar;
}

5、string 转double

double toolC::string2num(std::string str)
{
    double num = 0.0;
    std::stringstream ss;
    ss << str;
    ss >> num;
    return num;
}

6、double 转string

string toolC::num2string(double num)
{
    stringstream ssdouble;
    ssdouble << num;
    string str = ssdouble.str();
    return str;
}

7、long double 转string

string toolC::do_fraction(long double value, int decplaces)
{
    ostringstream out;
    int prec = numeric_limits<long double>::digits10;

    out.precision(prec);//覆盖默认精度
    out << value;
    string str = out.str();//从流中取出字符串
    size_t n = str.find(".");
    if((n != string::npos) /有小数点
        && (str.size() > n + decplaces))//还有至少decplaces位
    {
        str[n + decplaces] = '\0';//覆盖第一个多余的数
    }
    
    str.swap(string(str.c_str());//删除nul之后的多余字符

    return str;
}