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    <p>This is highly dependent on the compiler and platform you are using and without actually seeing the tests I can only guess of what is going on.<br /><br /> I see some misconceptions in your code:<br /> 1) You are missing a copy operator and copy constructor You are copying the instances that contain <code>std::string</code> which might be implemented using reference counting. The reference counting is implemented in overloaded copy constructor/operator of <code>std::string</code> but these might not get called from the implicitly generated copy constructor of your class and therefore causing double freed memory and other nasty things. The copy operator/constructor should look like this:</p> <pre><code>// Copy constructor Parms(const Parms&amp; oth) { parm1 = oth.parm1; parm2 = oth.parm2; } // Copy operator Parms&amp; operator= (const Parms&amp; oth) { if (&amp;oth == this) // Check for self-assignment return *this; parm1 = oth.parm1; parm2 = oth.parm2; return *this; } </code></pre> <p><br /><br /> 2) I don't quite understand the presence of <code>value1</code> and <code>value2</code>. It seems you never initialize them, you just use them in the default constructor to copy their (empty) content into <code>parm1</code> and <code>parm2</code>. You can avoid this completely as <code>parm1</code> and <code>parm2</code> are initialized automatically to an empty string when called. <br /><br /> 3) You do not need to use the singleton pattern here. The <code>getDefaults()</code> method could be implemented as follows:</p> <pre><code>static Parms getParms() { return Parms(); } </code></pre> <p>The singleton pattern is meant for classes that only have one instance through the whole program run which doesn't seem to be the case of your class.</p> <p>This way you can safely use the <code>getParms()</code> function from multiple threads and a smart compiler will optimize out the implied additional copy.</p>
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    1. POCorrupted singleton data using CxxTest
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    1. USKarel Petranek
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    1. COSorry, I should have been more explicit in my original question. This is an issue I ran across at work, so I wasn't about to copy & paste the actual code, so what I put together was (an apparently not that clear) trivialized example. The singleton behavior is used because there is also a setDefaults() method, so you can set them once and then reuse them wherever. At any rate, the real problem was #1. I did not realize that the std::string implementation used refcounting, so I assumed a shallow copy would be valid. Thanks for your response.
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      1. USPaul D.
    2. COActually wait a second. Why would it being refcounted blow everything up? If I call getDefaults() and assign it into some of type Parms, it ought to just increase the refcount, and then later when the test ends and it goes out of scope, it ought to decrease it, and life should go on as normal.
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      1. USPaul D.
    3. COOh I see what you are saying. Is there some definitive spec to look at that nails down what all the possible copy constructors and assignment operators are? It seems odd to me that they would design things in such a way that you could accidentally invalidate the refcount.
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