C++/CLI - URL 下载到文件

Question

我并不完全熟悉 CLI 的工作原理，但我有一个大概的概念。我有一个函数需要 2 个 System::String 变量，并使用它们从网页下载文件。就下载而言，它工作正常，文件显示在我的目录中，包含必要的内容。但是，它给了我错误

An unhandled exception of type 'System.AccessViolationException' occurred in ParseLinks.exe

void downloadFile(System::String ^_URL, System::String ^_saveAs)
{
    try
    {
        System::Net::WebClient ^webClient = gcnew System::Net::WebClient();
        // Downloads the resource with the specified URI to a local file.
        webClient->DownloadFile(_URL, _saveAs);
        webClient->Dispose();
    }
    catch (System::Exception ^_e)
    {
        // Error
        System::Console::WriteLine("Exception caught in process: {0}", _e);
    }
}

我做了一些挖掘和输出测试，发现 exe 在文本文件的某处遇到断点，因为整个网页没有保存到 txt 文件。

相关代码:

        if (myFile.is_open()) //if file open
        {
            while (!myFile.eof()) //before end of file
            {
                getline(myFile, ln);
                lines[count] = ln;
                count++; //count total lines to set loop length for later parsing
                //Error occurs somewhere in here
            }
            myFile.close();
        }
        else
            cout<<"Error: Could not access file\n";

全新错误! :(

An unhandled exception of type 'System.Runtime.InteropServices.SEHException' occurred in ParseLinks.exe

文件后的代码->线数组循环

myFile.close(); //Close txt file

            //Loop through lines
            for (int i = 0; i < count; i++)
            {
                string temp = parseLinks(lines[i]); //parse links from each line

那个函数:

string parseLinks(string str)
{
    const int len = str.length();
    string link;
    bool quotes = false, islink = false;
    string compare[5] = {".htm",".html",".php",".asp",".pdf"};

    //Parse all quoted text
    for (int i = 0; i != len; i++)
    {
        //Change bool if quote found
        if (str[i] == '"')
        {
            if (quotes == false)
                quotes = true;
            else
                quotes = false;
        }

        //If bool true, and char is not a quote, add to link string
        if (quotes == true && str[i] != '"')
            link += str[i];
    }

    //Discard non-link text
    for (int i = 0; i < 5; i++)
    {
        //Link check for links given array of path filetypes
        if (link.compare((link.length() - compare[i].length()),compare[i].length(),compare[i]) == 0)
            islink = true;
    }
    //Link check for links with no path filetype (.html, .php, etc.)
    if (link.compare(0,7,"http://") == 0)   
        islink = true;

    //If not a link, return empty string
    if (islink == false)
        link = "";

    return link;
}

错误指向我在这个函数中的大型比较语句。 (此外，我在压缩代码方面显然很糟糕)

Answer 1

您错误地使用了 getline，这可能导致了您的错误。正确的成语是这样的:

std::string line;
while (std::getline(myFile, line))
{
  // process `line`
}

无需单独检查myFile的开放性。