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    <p>As 6502 explained, it is not possible to do this in portable C without some kind of context argument being passed to the callback, even if it doesn't name <code>secret_id</code> directly. However, there are libraries such as <a href="http://www.gnu.org/software/libffcall/trampoline.html" rel="nofollow">Bruno Haible's trampoline</a> that enable creation of C functions with additional information (closures) through non-portable means. These libraries do their magic by invoking assembly or compiler extensions, but they are ported to many popular platforms; if they support architectures <em>you</em> care about, they work fine.</p> <p>Taken from <a href="http://www.stackprinter.com/export?service=stackoverflow&amp;question=644246&amp;printer=false&amp;linktohome=true" rel="nofollow">the web</a>, here is an example of code that trampoline enables is this higher-order function that takes parameters <code>a</code>, <code>b</code>, and <code>c</code> (analogous to your <code>secret_id</code>, and returns a function of exactly one parameter <code>x</code> that calculates <code>a*x^2 + b*x + c</code>:</p> <pre><code>#include &lt;trampoline.h&gt; static struct quadratic_saved_args { double a; double b; double c; } *quadratic_saved_args; static double quadratic_helper(double x) { double a, b, c; a = quadratic_saved_args-&gt;a; b = quadratic_saved_args-&gt;b; c = quadratic_saved_args-&gt;c; return a*x*x + b*x + c; } double (*quadratic(double a, double b, double c))(double) { struct quadratic_saved_args *args; args = malloc(sizeof(*args)); args-&gt;a = a; args-&gt;b = b; args-&gt;c = c; return alloc_trampoline(quadratic_helper, &amp;quadratic_saved_args, args); } int main() { double (*f)(double); f = quadratic(1, -79, 1601); printf("%g\n", f(42)); free(trampoline_data(f)); free_trampoline(f); return 0; } </code></pre>
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    1. POEmulating std::bind in C
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    1. COClosures are indeed the way to achieve this in "C". LibFFI provides closures and is portable to most major OSs: http://sourceware.org/libffi/
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      1. USBojan Nikolic
    2. CO@BojanNikolic Good point, and libffi is much more popular than trampoline. An answer with na example that solves the OP's problem using libffi might be appreciated.
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