The following short C program can be compiled gcc test.c -lmpg123 and run without error: 

#include <stdio.h>
#include <mpg123.h>

int main (void) {
    int check = mpg123_init();
    if (check != MPG123_OK)
        fprintf(stderr,"fail: %s\n", mpg123_plain_strerror(check));
    return 0;
}

[download]

And yet, on the exact same system, the following perl program fails with undefined symbol: mpg123_init, indicating libmpg123 has not been linked: 

#!/usr/bin/perl
use strict;
use warnings FATAL => qw(all);

use Inline 'C' => Config =>
    CLEAN_AFTER_BUILD => 0,
    LIBS => '-lmpg123';
use Inline 'C';
Inline->init();

test();

__DATA__
__C__
#include <mpg123.h>

void test () {
    fprintf(stderr,"%d\n", mpg123_init());
}

[download]

If I add -L/usr/local/lib to LIBS, then everything works out.

However, ld --verbose output includes SEARCH_DIR("/usr/local/lib") -- notice, I did not need an to use -L when compiling the C version -- and for what it's worth, ldconfig also includes /usr/local/lib in the runtime path. This means Inline::C or MakeMaker is doing its own thing when looking for the libraries; if I look at the Makefile in the _Inline/build directory, the "MakeMaker const_loadlibs section", which should contain the stuff from LIBS, is empty (unless I use -L). A comment there refers to the ExtUtils::Liblist pod, where EXTRALIBS (from this same section of the Makefile) is described:

List of libraries that need to be linked with when linking a perl binary which includes this extension. Only those libraries that actually exist are included.

But no explanation for how the (non-)existence of a library is determined.

Obviously, I cannot deploy this (without requiring the source be edited on each system) if I cannot be certain that Inline::C will find libraries which are otherwise accessible by the normal rules. Any form of insight is appreciated.

In reply to Perplexed by Inline::C/MakeMaker LD path by halfcountplus

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