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POC++, is linking order standardized?
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  1. POC++, is linking order standardized?
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    copied!<p>On my linux box, I have 2 libraries: </p> <pre><code>libfoo1.a and libfoo2.a </code></pre> <p>and they both contain an implementation of </p> <pre><code>void foo(int) </code></pre> <p>and my main program calls foo:</p> <pre><code>int main() { foo(1); return 0; } </code></pre> <p>I compiled the program two ways using g++</p> <pre><code>g++ main.cpp libfoo1.a libfoo2.a -o a1.out g++ main.cpp libfoo2.a libfoo1.a -o a2.out </code></pre> <p>When I run the programs, a1 is clearly using the foo() implementation from libfoo1.a, while a2 clearly used libfoo2. That is, g++ linked whichever foo() that it saw first.</p> <p>My question (finally) is, is this "greedy" linking policy actually specified in the C++ standard? Or would a different compiler / platform behave differently in an implementation-defined way?</p> <p>PS: To put the question in practical context, I really like the way this g++ example works. In my real application, I have a legacy libfoo2 that implements many (many!) functions, but I want to provide new implementations for a handful of them in libfoo1. On one hand I could write a whole new interface in libfoo1, implement my handful, then delegate to libfoo2 for the remainder. But I would rather void writing all that delegation code, if I can rely linker to do it for me (even for non-g++ compilers like icc).</p> <p>PPS: To put it in <em>real</em> practical context, libfoo2 is the blas, and libfoo1 is a homebrew OpenMP implementation of a few of its routines. I'm not ready to shell out for MKL. ATLAS does not multithread the functions I want to call. It is very good at multithreading GEMM, but I need some of the quirkier routines from LAPACK to be fast too (zsptrf / zsptrs / zspr). It appears that the my cache-ignorant OpenMP implementation of these routines can do better than it's cache-tuned sequential implementation. </p> <p>Sorry for the length of post.</p>
 

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