如何循环BSTR？

Question

我有一个BSTR，里面有很多的混血儿。

        BSTR theFile = NULL;
        int res = comSmartspeak -> readTheFile(fileName, &theFile);

我想读第一行，但我不知道怎么做。

这是我想出的pseudoCode：

        string firstLine = "";
        for (int i = 0; i < SysStringLen(theFile) ; i++)
        {
            if (theFile[i] == '\n')
            {
                break;
            }else
            {
                firstLine += theFile[i] ;
            }
        }

我是VC++的新手。

Answer 1

//another option

BSTR comStr = ::SysAllocString(L"First line of text\nSecond line of text\nThird line of text\nFourth line of text...");

    std::wstring ws(comStr, SysStringLen(comStr));

    std::wstring::size_type pos = ws.find_first_of('\n');
    if (pos != std::wstring::npos)
    {
        std::wcout << ws.substr(0, pos);
    }

Answer 2

您可以这样做，前提是您可以自由地使用std::wstring，这样您就不必事先计算第一行的长度：

#include <Windows.h>
#include <iostream>
#include <string>

int main()
{
    BSTR a_bstr = ::SysAllocString(L"First line of text\nSecond line of text\nThird line of text\nFourth line of text...");
    std::wstring wide_str;
    unsigned int len = ::SysStringLen(a_bstr);
    for (unsigned int i = 0; i < len; ++i)
    {
        if (a_bstr[i] != '\n')
            wide_str += a_bstr[i];
        else
            break;
    }

    // wide_str holds your first line
    std::wcout << "First line: " << wide_str << std::endl;
    ::SysFreeString(a_bstr);
    return 0;
}