libcurl 404检测 我在我的C++程序中用LIbCURL进行文件下载。如何检测请求是否为404，而不执行文件写入？代码是： void GameImage::DownloadImage(string file_name) { string game_name; game_name = file_name.substr(file_name.find_last_of("/")+1); CURL *curl; FILE *fp; CURLcode res; string url = "http://site/"+game_name+".png"; string outfilename = file_name+".png"; cout<<"INFO; attempting to download "<<url<<"..."<<endl; curl = curl_easy_init(); if (curl) { cout<<"INFO; downloading "<<url<<"..."<<endl; fp = fopen(outfilename.c_str(), "wb"); cout<<"INFO; trying to open "<<outfilename<<" for file output"<<endl; if (fp != NULL) { curl_easy_setopt(curl, CURLOPT_URL, url.c_str()); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, GameImage::WriteData); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); curl_easy_setopt(curl, CURLOPT_VERBOSE, 1); curl_easy_setopt(curl, CURLOPT_FAILONERROR, true); res = curl_easy_perform(curl); long http_code = 0; curl_easy_getinfo (curl, CURLINFO_RESPONSE_CODE, &http_code); curl_easy_cleanup(curl); fclose(fp); } else { cout<<"GameImage::DownloadImage; Couldn't open output file"<<endl; } } } size_t GameImage::WriteData(void *ptr, size_t size, size_t nmemb, FILE *stream) { size_t written; written = fwrite(ptr, size, nmemb, stream); return written; } void GameImage:：DownloadImage（字符串文件名）{ 字符串游戏名称； game\u name=file\u name.substr（file\u name.find\u last\u of（“/”）+1）； 卷曲*卷曲； 文件*fp； 卷曲编码； 字符串url=”http://site/“+游戏名称+”.png”； 字符串outfilename=文件名+“.png”； cout

您可以检查

CURLE\u HTTP\u返回的\u错误

---

如果

CURLOPT\u FAILONERROR

设置为

true

，HTTP服务器返回的错误代码为

=400

。您无法获取特定的HTTP响应代码，但应该足以完成所需的操作。

我知道这是一篇旧文章，但您所做的错误是没有检查retcurl_easy_perform的urn值。设置CURLOPT_FAILONERROR不会使程序崩溃，相反，它会通过名为res的返回变量通知您错误。要清除空文件，可以执行以下操作：

void GameImage::DownloadImage(string file_name) {
    string game_name;
    game_name = file_name.substr(file_name.find_last_of("/")+1);

    CURL *curl;
    FILE *fp;
    CURLcode res;
    string url = "http://site/"+game_name+".png";
    string outfilename = file_name+".png";
    cout<<"INFO; attempting to download "<<url<<"..."<<endl;
    curl = curl_easy_init();
    if (curl) {
        cout<<"INFO; downloading "<<url<<"..."<<endl;
        fp = fopen(outfilename.c_str(), "wb");
        cout<<"INFO; trying to open "<<outfilename<<" for file output"<<endl;
        if (fp == NULL) {
            cout<<"GameImage::DownloadImage; Couldn't open output file"<<endl;
            curl_easy_cleanup(curl);
            return;
        }
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, GameImage::WriteData);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
        curl_easy_setopt(curl, CURLOPT_FAILONERROR, true);
        res = curl_easy_perform(curl);
        fclose(fp);

        if (res != CURLE_OK) {
            cout<<"GameImage::DownloadImage; Failed to download file"<<endl;
            remove(outfilename.c_str());
        }

        curl_easy_cleanup(curl);
    }
}

size_t GameImage::WriteData(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written;
    written = fwrite(ptr, size, nmemb, stream);
    return written;
}

void GameImage:：DownloadImage（字符串文件名）{
字符串游戏名称；
game\u name=file\u name.substr（file\u name.find\u last\u of（“/”）+1）；
卷曲*卷曲；
文件*fp；
卷曲编码；
字符串url=”http://site/“+游戏名称+”.png”；
字符串outfilename=文件名+“.png”；
我仍然可以得到一个文件，但它现在是空的。我添加了curl\u easy\u setopt（curl，CURLOPT\u FAILONERROR，true）；我不在乎是否发生了错误，我只是不希望文件被留下。我想这是因为创建文件句柄的初始fp=fopen（outfilename.c_str（），“wb”）；它创建了文件句柄。