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<overview>

<p>This metric measures the number of public global variables in a file.</p>

<p>Global variables can cause several problems:</p>

<ul>

<li>lack of encapsulation, because state is exposed to the whole program, rather than a single module</li>

<li>difficulty maintaining the software, because code using or manipulating the value of the global may be scattered across the software, so its hard to track them all down when making a change</li>

<li>defects in multi-threading, because the code that uses globals is usually not thread-safe</li>

</ul>

</overview>

<recommendation>

<p>Make global variables local to a file, and provide functions for manipulating the

value of the variable in a thread-safe way. If possible, make the variable an instance

variable in a class or struct that is passed from function to function as necessary so

that there is no global state.</p>

</recommendation>

<references>

<li>

<a href="http://www.learncpp.com/cpp-tutorial/42-global-variables/">Global variables</a>

</li>

<li>

<a href="http://www-h.eng.cam.ac.uk/help/tpl/languages/C++/globals.html">C++: Global warning</a>

</li>

<li>

<a href="https://www.securecoding.cert.org/confluence/display/c/DCL19-C.+Minimize+the+scope+of+variables+and+functions">Minimize the scope of variables and functions</a>

</li>

</references>

</qhelp>