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hey everybody today I want to talk about have you ever been coding along programming minding your own business all of a sudden you run your program and you get this big nasty error and you look through it and to the beginner this deluge of error information probably means about as much to you as the most obscure IRS tax form around and so today we're gonna try to break it down and make some sense out of it so specifically let's look closer there are a few hints that it gives us first of all I mentioned free okay so maybe maybe this has something to do with allocating memory it also has a back-trace which because it's all in Lib C probably doesn't mean much to you and it has a memory map which also at this stage assuming you're a beginner probably doesn't mean a whole lot to you all this really means though is that you broke the heat and this is the heaps cry for help in case you're not familiar with the heat the heap is essentially the region in memory where blocks get allocated when you call malloc calloc realloc and then they're released when you call free so these blocks of memory are usually just stacked up next to each other there's other information that may be stored between blocks describing how big blocks are or offsets to the next block so it helps you keep track of everything that's in this heap so this is basically a big just jumble of data that you've requested and it's handing it out in chunks of different sizes and you can put anything you want in these blocks you can copy from one block to another you can you can store binary data or text data it really doesn't matter the problem is is that there's nothing that prevents you from over running the end of the blocks let's say you're just putting data into one of these blocks the block is size 40 and you decide to put 80 or 90 or a hundred or a thousand bytes into this block there's nothing that stops you from doing that but essentially what you did is you just stomped on a bunch of other blocks you stomped on a bunch of metadata white block sizes and things like that and so at some point probably during a malloc or free call the allocator tries to read some of its memory it doesn't make any sense and so it basically just throws its hands up and says I don't know what happened fix me and now if we look back at that error messages it actually makes sense because you get some message like invalid next size and basically what it was expecting was the next size telling you what size the next block is but the size that it read doesn't make any sense be we clobbered it with something else as in...