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POC macros independent of type specifier
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  1. POC macros independent of type specifier
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    copied!<p>How can I write a Standard C( C89 or C99 compliant) macro that is <em>independent of type specifier</em>?</p> <p>Specifically, I want to write a macro <em>to compare two numbers which can be of signed type or unsigned type, 8-bits, 16-bits, 32-bits, 64-bits.</em></p> <p>What I'm looking for, is something like this:</p> <pre><code> int c, a , b; uint16_t p, q, r; . . . c = min(a, b); . . . r = min(p, q); . . . </code></pre> <p>ie, <em>the same macro 'min' can be used to compare two integers - any width, signed or unsigned.</em> </p> <p>I know that a basic macro that work can be written like this:</p> <pre><code> #define min(x, y) (x) &lt; (y) ? (x) : (y) </code></pre> <p>But this involves <em>side-effect of evaluating expressions 'x' and 'y' twice</em>, which I don't want.</p> <p>For robustness, expressions must be evaluated once only.</p> <p>Till now, my approach seems like this:</p> <pre><code> #define min(type, x, y) ( { \ type __tmp1 = (x); \ type __tmp2 = (y); \ __tmp1 &lt; __tmp2 ? __tmp1 : __tmp2; } ) int a, b, c; uint16_t p, q, r; . . . c = min(int, a, b); </code></pre> <p>The C compiler throws error: "expecting ; found ( ", and many others.</p> <p>How can I re-write this macro so that is <em>usage</em> take this form :</p> <pre><code> &lt;result&gt; = min( &lt;type&gt;, &lt;parm1&gt;, &lt;parm2&gt; ); </code></pre> <p>It seems that 'min' macro can be written so that its usage is:</p> <pre><code> min( &lt;result&gt;, &lt;type&gt;, &lt;parm1&gt;, &lt;parm2&gt; ); </code></pre> <p>But it would be nice to have first form.</p> <p><strong>Update#1 on 2012-09-04:</strong></p> <p>Thank you guys, all the info provided in your answers/comments gave me a wider perspective of possibilities. Well, I am not using gcc, neither my compiler supports C11 spec, so the only options that seem to be available are:</p> <ol> <li><p>Use this form of macro:</p> <pre><code> // min( &lt;result&gt;, &lt;type&gt;, &lt;parm1&gt;, &lt;parm2&gt; ); #define min(result, type, x, y) { \ type __tmp1 = (x); \ type __tmp2 = (y); \ result = __tmp1 &lt; __tmp2 ? __tmp1 : __tmp2; } int p, q, r; . . . min(r, int, p, q); </code></pre></li> <li><p>The other approach is :</p> <pre><code> inline char min_char(char x, char y) { return x &lt; y ? x : y; } inline short min_short(short x, short y) { return x &lt; y ? x : y; } inline int min_int(int x, int y) { return x &lt; y ? x : y; } inline long min_long(long x, long y) { return x &lt; y ? x : y; } inline unsigned char min_uchar(unsigned char x, unsigned char y) { return x &lt; y ? x : y; } inline unsigned short min_ushort(unsigned short x, unsigned short y) { return x &lt; y ? x : y; } inline unsigned int min_uint(unsigned int x, unsigned int y) { return x &lt; y ? x : y; } inline unsigned long min_ulong(unsigned long x, unsigned long y) { return x &lt; y ? x : y; } #define min(type, x, y) min_##type(x, y) int p, q, r; . . . r = min(int, p, q); </code></pre></li> </ol> <p>Are there any side-effects of 2nd approach, that might yield unexpected results in some cases, especially regarding 'short' and 'char' types - signed or unsigned.</p> <p>Any improvements or suggestions are welcome.</p> <p><strong>EDITED:</strong> </p> <p>How will the user specify the below function:</p> <pre><code> 'min_uchar' </code></pre> <p>He/she must write:</p> <pre><code> r = min(uchar, p, q); </code></pre> <p>Is there any other way to write the function 'uchar', so that user can simply write:</p> <pre><code> r = min(unsigned char, p, q); </code></pre> <p>In this case I can't name the function as 'min_unsigned char', as it is not allowed in C. Is there any other way or user will have to specify type as 'uchar' instead of 'unsigned char' in macro 'min'.</p> <p><strong>Update on 2012-09-10:</strong></p> <p>Thank you all guys for your help. Since I need to accept an answer, I'm accepting <em>Eitan T</em>'s answer, but I appreciate responses from all of you. Thanks.</p>
 

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