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