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copied!<p>When you mix C and C++ code together, you can run into trouble because the two languages have different <em>linkages</em>. That is, if you were to crack open the object files for a compiled C and C++ file, you would find that the names inside of those object files were different.</p> <p>In particular, C++ compilers tend to use a technique called "name mangling" in which function names are mixed with extra information about the types of their arguments. For example, a function</p> <pre><code>char foo(int); </code></pre> <p>might actually have the internal name</p> <pre><code>char@foo@int </code></pre> <p>inside of the generated object file. The problem is that C code does not do this, so if you compiled a C file and tried to make a reference to the name <code>foo</code>, the linker wouldn't find it, because the name of the function in the generated C++ file is <code>char@foo@int</code> instead of <code>foo</code>.</p> <p>To fix this, C++ has a feature that allows you to explicitly tell the linker not to mangle the name and to make the generated code look like it was intended for a C program. To do this, you can declare C++ functions like this:</p> <pre><code>extern "C" char foo(int); </code></pre> <p>Now, the generated object file will contain the name <code>foo</code> without adornment in a way that is compatible with what the C code expects.</p> <p>To fix your problem, try adding one of these <code>extern "C"</code> declarations to your C++ source file that defines <code>reciprocal</code>.</p> <p>A note: if you have a project that mixes C and C++ code, you should <em>always</em> have the <code>main</code> function compiled as C++ code. C++ introduces extra initialization and cleanup code into its executables that are not present in C code. If you compile <code>main</code> as C code, this extra logic might not get added into the program, and so you may get inexplicable crashes at runtime.</p> <p>Hope this helps!</p>

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