“void *”类型的值不能用于初始化“callback_data *”类型的实体

问题描述

我正在尝试运行此 Code 并出现错误：

    Severity    Code    Description Project File    Line    Suppression State
    Error (active)  E0144   a value of type "void *" cannot be used to initialize an entity of type "callback_data *"

 static size_t write_it(char *buff,size_t size,size_t nmemb,void *cb_data)
    {
      struct callback_data *data = cb_data; // ERROR
      size_t written = 0;
      if(data->output)
        written = fwrite(buff,size,nmemb,data->output);
      else
        /* listing output */
        written = fwrite(buff,stdout);
      return written;
    }

我使用的是 VS2019，C++ // 完整代码

#include <curl/curl.h>
#include <stdio.h>
 
struct callback_data {
  FILE *output;
};
 
static long file_is_coming(struct curl_fileinfo *finfo,struct callback_data *data,int remains);
 
static long file_is_downloaded(struct callback_data *data);
 
static size_t write_it(char *buff,void *cb_data);
 
int main(int argc,char **argv)
{
  /* curl easy handle */
  CURL *handle;
 
  /* help data */
  struct callback_data data = { 0 };
 
  /* global initialization */
  int rc = curl_global_init(CURL_GLOBAL_ALL);
  if(rc)
    return rc;
 
  /* initialization of easy handle */
  handle = curl_easy_init();
  if(!handle) {
    curl_global_cleanup();
    return CURLE_OUT_OF_MEMORY;
  }
 
  /* turn on wildcard matching */
  curl_easy_setopt(handle,CURLOPT_WILDCARDMATCH,1L);
 
  /* callback is called before download of concrete file started */
  curl_easy_setopt(handle,CURLOPT_CHUNK_BGN_FUNCTION,file_is_coming);
 
  /* callback is called after data from the file have been transferred */
  curl_easy_setopt(handle,CURLOPT_CHUNK_END_FUNCTION,file_is_downloaded);
 
  /* this callback will write contents into files */
  curl_easy_setopt(handle,CURLOPT_WRITEFUNCTION,write_it);
 
  /* put transfer data into callbacks */
  curl_easy_setopt(handle,CURLOPT_CHUNK_DATA,&data);
  curl_easy_setopt(handle,CURLOPT_WRITEDATA,&data);
 
  /* curl_easy_setopt(handle,CURLOPT_VERBOSE,1L); */
 
  /* set an URL containing wildcard pattern (only in the last part) */
  if(argc == 2)
    curl_easy_setopt(handle,CURLOPT_URL,argv[1]);
  else
    curl_easy_setopt(handle,"ftp://example.com/test/*");
 
  /* and start transfer! */
  rc = curl_easy_perform(handle);
 
  curl_easy_cleanup(handle);
  curl_global_cleanup();
  return rc;
}
 
static long file_is_coming(struct curl_fileinfo *finfo,int remains)
{
  printf("%3d %40s %10luB ",remains,finfo->filename,(unsigned long)finfo->size);
 
  switch(finfo->filetype) {
  case CURLFILETYPE_DIRECTORY:
    printf(" DIR\n");
    break;
  case CURLFILETYPE_FILE:
    printf("FILE ");
    break;
  default:
    printf("OTHER\n");
    break;
  }
 
  if(finfo->filetype == CURLFILETYPE_FILE) {
    /* do not transfer files >= 50B */
    if(finfo->size > 50) {
      printf("SKIPPED\n");
      return CURL_CHUNK_BGN_FUNC_SKIP;
    }
 
    data->output = fopen(finfo->filename,"wb");
    if(!data->output) {
      return CURL_CHUNK_BGN_FUNC_FAIL;
    }
  }
 
  return CURL_CHUNK_BGN_FUNC_OK;
}
 
static long file_is_downloaded(struct callback_data *data)
{
  if(data->output) {
    printf("DOWNLOADED\n");
    fclose(data->output);
    data->output = 0x0;
  }
  return CURL_CHUNK_END_FUNC_OK;
}
 
static size_t write_it(char *buff,void *cb_data)
{
  struct callback_data *data = cb_data; // ERROR
  size_t written = 0;
  if(data->output)
    written = fwrite(buff,data->output);
  else
    /* listing output */
    written = fwrite(buff,stdout);
  return written;
}

解决方法

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