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POgdb and debugging problems with an STL list
 

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    <p>I recently asked a question here, and didn't get an answer I could use, unfortunately:</p> <p><a href="https://stackoverflow.com/questions/14899678/c-stl-list-functions-segfaulting-with-empty-list">C++ STL list functions segfaulting with empty list</a></p> <p>I've been trying to use gdb to debug the issue, and I have a question about what something means:</p> <p>I declare a list as a member of a class like so:</p> <pre><code>std::list&lt;Thing*&gt; inventory; </code></pre> <p>...and then instantiate the class it's in (an object called 'pc'). In gdb, I presume this shows that I have some memory allocated to it?</p> <pre><code>(gdb) p &amp;pc.inventory $7 = (std::list&lt;Thing*, std::allocator&lt;Thing*&gt; &gt; *) 0xbffff22c </code></pre> <p>Further in, one line before the problem line of the code (in essence, calling 'inventory.size()' causes a segfault), this still holds:</p> <pre><code>(gdb) p &amp;inventory $8 = (std::list&lt;Thing*, std::allocator&lt;Thing*&gt; &gt; *) 0xbffff22c </code></pre> <p>...however I still get the segfault:</p> <pre><code>(gdb) n 558 if (inventory.size() == 52) { (gdb) n Program received signal SIGSEGV, Segmentation fault. 0x0804e3fe in std::_List_const_iterator&lt;Thing*&gt;::operator++ (this=0xbfff94e0) at /usr/include/c++/4.4/bits/stl_list.h:223 223 _M_node = _M_node-&gt;_M_next; </code></pre> <p>My question is essentialy this: Surely, if I have an address for the member list, the list exists, and I should be able to use size() on it?? If not, why not? And how could I further debug?</p> <p>Thanks all!</p>
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    1. COJust because something has a non-null address doesn't mean it's a valid address. C++ doesn't set pointers to null when initialized or invalidated, it just uses what's in the memory at that time. From what you've shown this could very well be the problem. Construct a minimal test case that reproduces the problem and we may be able to help.
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    2. COThanks, Dukeling, I did that, and have found the root of the issue. Still don't know how to fix it though! Here it is: http://stackoverflow.com/questions/15133520/array-setup-in-constructor-means-failure-later-on
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