realloc的（）：无效的下一个大小 [英] realloc(): invalid next size

问题描述

我在用realloc函数的一个问题。我使用的是libcurl的仅C（所以没有载体）。我遇到的问题是，我发现了以下错误（realloc的（）：无效的下一个大小）上WRITE_DATA功能（我通过卷曲作为回调函数的迭代12日，它被称为每次都有的libcurl一些数据传回（数据以块的形式传递））。

I'm having a problem with the realloc function. I'm using C only (so no vector) with LibCurl. The problem I'm having is that I'm getting the following error (realloc(): invalid next size) on the 12th iteration of the write_data function (the function I pass to Curl as a callback, it is called each time libcurl has some data to pass back (data is passed in chunks) ).

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#include <stdio.h>
#include <stdlib.h>
#include <curl/curl.h>
#include <string.h>

char * Data; //stores the data
size_t  RunningSize;

int write_data( char *ptr, size_t size, size_t nmemb, void *stream )
{
    size_t ThisSize = (size * nmemb); //Stores the size of the data to be stored
    size_t DataLen = strlen( Data ); //length of the data so far

    RunningSize = (RunningSize + ThisSize ); //update running size (used as new size)

   Data = realloc( Data, RunningSize ); //get new mem location (on the 12th iteration, this fails)
   strcat( Data, ptr); //add data in ptr to Data

    return ThisSize; //the function must return the size of the data it received so cURL knows things went ok.
}

int main( )
{
  CURL *curl;
  CURLcode res;
  const char * UserAgent = "";

  Data = malloc(1); //so realloc will work
  RunningSize += 1;

  curl = curl_easy_init();
  if(curl)
  {
    curl_easy_setopt( curl, CURLOPT_NOBODY, 0 );
    curl_easy_setopt( curl, CURLOPT_URL, "http://www.google.co.uk/" );
    curl_easy_setopt( curl, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt( curl, CURLOPT_USERAGENT, UserAgent );
    curl_easy_setopt( curl, CURLOPT_HEADER, 1 );

    //preform request.
    res = curl_easy_perform(curl);

    //output the data (debugging purposes)
    puts( Data );

    //cleanup
    curl_easy_cleanup(curl);
    free(Data);
  }

  return 0;
}

由于提前，

推荐答案

在传递给数据WRITE_DATA（）不一定是空终止的;这就是为什么它会告诉你的字节数。

The data passed in to write_data() isn't necessarily nul-terminated; that's why it tells you the number of bytes.

这意味着你不能使用的strcat（）。使用它是运行了数组的末端，破坏由的malloc / 的realloc 使用的数据结构，因此错误

This means you can't use strcat(). Using it is running off the end of the array and corrupting the data structures used by malloc / realloc, hence the error.

您 WRITE_DATA（）应使用的memcpy（）代替，像这样：

Your write_data() should use memcpy() instead, like so:

int write_data( char *ptr, size_t size, size_t nmemb, void *stream )
{
    size_t ThisSize = (size * nmemb); //Stores the size of the data to be stored
    size_t DataLen = RunningSize; //length of the data so far

    RunningSize = (RunningSize + ThisSize ); //update running size (used as new size)

    Data = realloc( Data, RunningSize ); //get new mem location (on the 12th iteration, this fails)
    memcpy((char *)Data + DataLen, ptr, ThisSize); //add data in ptr to Data

    return ThisSize; //the function must return the size of the data it received so cURL knows things went ok.
}

您还需要 RunningSize 0，而不是1您可以初始化数据初始化为<$ C通过 NULL 到的realloc是允许的（）（并使其 - > NULL $ C表现就像的malloc（））。

You will also need to initialise RunningSize to 0, not 1. You can initialise Data to NULL - passing NULL to realloc() is allowed (and makes it behave just like malloc()).

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