我正在嘗試從 URL 收集一些資料。如果我沒有定義任何內容CURLOPT_WRITEFUNCTION，CURLOPT_WRITEDATA 我顯然可以在控制臺上看到輸出。然后我嘗試通過復制示例代碼將該資料寫入記憶體，但是我的回呼函式的 userdata 引數回傳NULL并且我在網上遇到了以下例外：
char* ptr = (char*)realloc(mem->memory, mem->size realsize 1);
Exception thrown: read access violation.
mem was nullptr.
難道我做錯了什么？
這是我的代碼：
struct MemoryStruct {
char* memory;
size_t size;
};
//-----------------
// Curl's callback
//-----------------
size_t CurlWrapper::curl_cb(char* data, size_t size, size_t nmemb, void* response)
{
size_t realsize = size * nmemb;
std::cout << "CALLBACK CALLED" << std::endl;
MemoryStruct* mem = (struct MemoryStruct*)response;
char* ptr = (char*)realloc(mem->memory, mem->size realsize 1);
if (!ptr) {
/* out of memory! */
printf("not enough memory (realloc returned NULL)\n");
return 0;
}
mem->memory = ptr;
memcpy(&(mem->memory[mem->size]), data, realsize);
mem->size = realsize;
mem->memory[mem->size] = 0;
return realsize;
}
//--------------------
// Do the curl
//--------------------
void CurlWrapper::curl_api(
const std::string& url,
std::string& str_result)
{
MemoryStruct chunk;
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &CurlWrapper::curl_cb);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void*)&chunk);
// TODO: enable ssh certificate
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, false); // true
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, false); // 2
curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "zlib");
auto res = curl_easy_perform(curl);
/* Check for errors */
if (res != CURLE_OK) {
// nothing
std::cout << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
}
}
}
libcurl 版本：7.82.0
uj5u.com熱心網友回復：
由于 libcurl 是一個 C 庫，它對 C 成員函式或物件一無所知。您可以使用例如傳遞指向類的指標的靜態成員函式相對輕松地克服此“限制”。
請參閱此示例（來自一切卷曲書）。
// f is the pointer to your object.
static size_t YourClass::func(void *buffer, size_t sz, size_t n, void *f)
{
// Call non-static member function.
static_cast<YourClass*>(f)->nonStaticFunction();
}
// This is how you pass pointer to the static function:
curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass::func);
curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
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