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POLinking error in simple C program using a C++ header
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copied!<p>I am following an intro tutorial <a href="http://www.linuxinsight.com/files/alp/alp-ch01-getting-started.pdf" rel="nofollow">http://www.linuxinsight.com/files/alp/alp-ch01-getting-started.pdf</a>.</p> <p>I have created the source files main.c, reciprocal.cpp and reciprocal.hpp. I have been able to successfully compile these files. The problem comes when I go to link them and I receive the following error message:</p> <pre><code>main.o: In function `main': main.c:(.text+0x30): undefined reference to `reciprocal' collect2: ld returned 1 exit status </code></pre> <p>I gather that this is somehow not using the header files correctly, however I do not really know what to try as I've followed the steps quite thoroughly.</p> <p>If anyone has an idea why its throwing that error I would appreciate it very much.</p> <p>Thanks</p> <p>**UPDATE Here is the code for the three source files:</p> <p>main.c</p> <pre><code>#include <stdio.h> #include "reciprocal.hpp" int main (int argc, char **argv) { int i; i = atoi(argv[1]); printf("The reciprocal of %d is %g\n", i, reciprocal(i)); return 0; } </code></pre> <p>reciprocal.cpp</p> <pre><code>#include <cassert> #include "reciprocal.hpp" double reciprocal(int i) { assert(i != 0); return 1.0/i; } </code></pre> <p>reciprocal.hpp</p> <pre><code>#ifdef __cplusplus extern "C" { #endif double reciprocal(int i); #ifdef __cplusplus } #endif </code></pre> <p>I have actually modified reciprocal.hpp since originally posting. The only change I've made was to remove the extern keyword from the function signature. It previously read </p> <pre><code>extern double reciprocal(int i); </code></pre> <p>This change allowed me to link the program and I can now run it. I think what may have been occurring is that the second extern was overriding the first one. If anyone has any insight on this, I would be interested in knowing.</p> <p>Thanks for your assistance everyone.</p>

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