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copied!<p>You seem to have them mixed up.</p> <p>You are right about </p> <pre><code>static const std::string Ten = "10"; </code></pre> <p>version. It will "work", but it will create a separate object in each translation unit. </p> <p>The version without <code>static</code> will have the same effect. It <em>won't</em> produce linker errors, but will define a separate object in each translation unit. In C++ language <code>const</code> objects have internal linkage by default, meaning that</p> <pre><code>const std::string Ten = "10"; // `static` is optional </code></pre> <p>is exactly equivalent to the previous version with <code>static</code>.</p> <p>The version with <code>extern</code> and initializer </p> <pre><code>extern const std::string Ten = "10"; // it's a definition! </code></pre> <p>will produce a <em>definition</em> of an object with external linkage (it is a definition because of the presence of an initializer). <em>This</em> version will result in linker errors, since you'll end up with multiple definitions of an object with external linkage - a violation of ODR.</p> <h3>Here's how you can do it:</h3> <p>In order to achieve what you are trying to achieve, you have to <em>declare</em> your constant in the header file</p> <pre><code>extern const std::string Ten; // non-defining declaration </code></pre> <p>and then define it (with initializer) in one and only one of the implementation files</p> <pre><code>extern const std::string Ten = "10"; // definition, `extern` optional </code></pre> <p>(If the constant is pre-declared as <code>extern</code>, then <code>extern</code> in the definition is optional. Even without an explicit <code>extern</code> it will define a const object with external linkage.)</p>

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