CODEWITHSUNDEEP
c++formscurldownload
Anonymous
Anonymous

Reputation: 553

Visual C++ Forms Application Error: C3374

I've been researching this for hours. I am VERY new to C++, and don't understand any solutions I have found thus far.

I'm trying to make a cURL file downloader in my form application, but I get this darn error:

Error   50  error C3374: can't take address of 'EmperorAntiVirusInstaller::FileDownloader::write_data' unless creating delegate instance    c:\users\bailey\documents\visual studio 2010\projects\emperor antivirus installer\emperor antivirus installer\FileDownloader.h  97

The code is as below:

private:
    size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
        size_t written;
        written = fwrite(ptr, size, nmemb, stream);
        return written;
    }
    System::Void beginDownload(void) {
        CURL *curl;
        FILE *fp;
        CURLcode res;
        char *url = "http://localhost/aaa.txt";
        char outfilename[FILENAME_MAX] = "C:\\bbb.txt";
        curl = curl_easy_init();
        if(curl) {
            fp = fopen(outfilename,"wb");
            curl_easy_setopt(curl, CURLOPT_URL, url);
            curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &FileDownloader::write_data);
            curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
            res = curl_easy_perform(curl);
            curl_easy_cleanup(curl);
            fclose(fp);
        }
    }

Additionally, the form's name is FileDownloader.

The erroring line is:

curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &FileDownloader::write_data);

I'm looking to find a nicely explained & simple answer on how to resolve this issue. :/

Upvotes: 0

Views: 621

Answers (1)

Jerry Coffin
Jerry Coffin

Reputation: 490108

You're trying to pass a pointer to a member function. It needs a pointer to a non-member function. You need to write a function that does what you need, but not as a member of a class.

At least if memory serves, if you just want the data written to the file you specify in your call with CURLOPT_WRITEDATA, you don't need to use CURLOPT_WRITEFUNCTION at all -- the default function will just write the data to the file you pass.

I suppose I should also mention, however, that (based on the mention of a delegate instance in the error message) you seem to be using C++/CLI instead of real C++. If that's the case, nearly everything else is probably open to at least a little question -- C++/CLI is quite a bit like C++ in some ways, but just enough different others to cause problems on a semi-regular basis.

Upvotes: 1

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