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<blockquote data-quote="Chris Torek" data-source="post: 2398169">The problem is isomorphic to:&nbsp; &nbsp; &quot;What kind of pointer should I use to point to either a char&nbsp; &nbsp; or a double, so that I can write *p = 3 to set the char to&nbsp; &nbsp; control-C or the double to 3.0?&quot;The answer is: there is no such pointer.&nbsp; You must change theproblem.In this case, the solution to the problem is to write a wrapperfunction.&nbsp; Since we know &quot;void *&quot; is a general-purpose datapointer, write a wrapper for fgetc():&nbsp; &nbsp; int wrap_fgetc(void *vp) {&nbsp; &nbsp; &nbsp; &nbsp; FILE *fp = vp;&nbsp; &nbsp; &nbsp; &nbsp; return fgetc(fp);&nbsp; &nbsp; }Assuming gzgetc() has type &quot;int gzgetc(void *)&quot;, you now have two&quot;int (void *)&quot; functions, and can point to either one with:&nbsp; &nbsp; int (*fp)(void *) = straight ? wrap_fgetc : gzgetc;Of course, you must also convert the argument as well:&nbsp; &nbsp; void *arg = straight ? the_fgetc_file : the_gzgetc_voidstar;If your second function (gzgetc, here) had some other pointertype as its sole parameter, you could wrap both functions, because&quot;void *&quot; will always be able to hold any other pointer.</blockquote>

[QUOTE="Chris Torek, post: 2398169"] The problem is isomorphic to: "What kind of pointer should I use to point to either a char or a double, so that I can write *p = 3 to set the char to control-C or the double to 3.0?" The answer is: there is no such pointer. You must change the problem. In this case, the solution to the problem is to write a wrapper function. Since we know "void *" is a general-purpose data pointer, write a wrapper for fgetc(): int wrap_fgetc(void *vp) { FILE *fp = vp; return fgetc(fp); } Assuming gzgetc() has type "int gzgetc(void *)", you now have two "int (void *)" functions, and can point to either one with: int (*fp)(void *) = straight ? wrap_fgetc : gzgetc; Of course, you must also convert the argument as well: void *arg = straight ? the_fgetc_file : the_gzgetc_voidstar; If your second function (gzgetc, here) had some other pointer type as its sole parameter, you could wrap both functions, because "void *" will always be able to hold any other pointer. [/QUOTE]

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