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POHow to elegantly implement a series of functions in different type versions using pure C?
 

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  1. POHow to elegantly implement a series of functions in different type versions using pure C?
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    <p>I want to write several functions that are only different in the types of arguments. I know C++ has <code>template</code> to handle this problem well (not very well yet though, few compilers support <code>export</code> keyword and this keyword is queried for efficiency). For easy example, I want:</p> <pre><code>template &lt;typename T&gt; T add(T a, T b){ return a+b; } </code></pre> <p>However, in pure C (sometimes I have to choose pure C, as some platform doesn't have the C++ compiler), there have to be different function names for different versions, as</p> <pre><code>double addDouble(double a, double b){ return a+b; } int addInt(int a, int b){ return a+b; } </code></pre> <p>Hmmm, when there are two versions, it seems OK that I can do the copy-and-paste work in a source file; However, in practice there would be many lines instead of just a <code>return</code> statement in a function and would be more versions. <strong>So, my question is, how to implement a series of functions in different type versions elegantly?</strong></p> <p>So far I have tried some solutions as below, but I think they are far from good. I need your suggestions, thank you!</p> <p><strong>Solution 1:</strong> </p> <pre><code>#define mytype int mytype addInt(mytype a, mytype b){ return a+b; } #undef mytype #define mytype float mytype addFloat(mytype a, mytype b){ return a+b; } #undef mytype </code></pre> <p><strong>Shortcoming of Solution 1:</strong> duplicated contents are too many, and if I want to modify the function, I have to modify all of versions.</p> <p><strong>Solution 2:</strong></p> <p><strong>func.h</strong></p> <pre><code>#ifndef FUNC_H #define FUNC_H #define add(a, b, typename) functionAdd##typename(a,b) /* function declarations */ #define declared(typename) \ typename functionAdd##typename(typename, typename) declared(int); declared(float); #endif </code></pre> <p><strong>func.c</strong></p> <pre><code>#include "func.h" /* function code */ #define functionAdd(a, b, typename) \ typename functionAdd##typename(typename a, typename b){ \ return a+b; \ } /* function bodies (definitions) */ functionAdd(a, b, int) functionAdd(a, b, float) </code></pre> <p><strong>main.c</strong></p> <pre><code>#include &lt;stdio.h&gt; #include "func.h" int main() { int x1 = add(1, 2, int); float x2 = add(3.0, 4.0, float); printf("%d %f\n", x1, x2); return 0; } </code></pre> <p><strong>Shortcoming of Solution 2:</strong> Because the function is written in <code>define</code>, it's difficult to debug. Besides, the <code>\</code> notation is annoying. Though, it's convenient to add a new version, just inserting <code>declared(double)</code> into func.h and <code>functionAdd(a, b, double)</code> into func.c will achieve this aim.</p>
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    1. CO@RedX - **Is there any other methods to do this work?** That's my question :)
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    2. CO@Stan: Re: "I know C++ has template to handle this problem well (not very well yet though..." Actually modern C++ compilers handle templates really well, and produce rather efficient code nowadays. Compile times for really complicated templates are a different matter. :-)
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    3. CO@In silico - In fact I'm talking about 'template definitions to be separated from their declarations' coding-style, the `export` keyword. See [wiki](http://en.wikipedia.org/wiki/C%2B%2B#Exported_templates). Forgive my poor English please.
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