From: Tor Erik Linnerud <tel@...>
Date: 2010-03-04T23:35:42+09:00
Subject: Re: Installing Pg gem for PostGreSQL 8.4

> checking for pg_config... yes
> checking for libpq-fe.h... yes
> checking for libpq/libpq-fs.h... yes
> checking for PQconnectdb() in -lpq... no
> checking for PQconnectdb() in -llibpq... no
> checking for PQconnectdb() in -lms/libpq... no
> Can't find the PostgreSQL client library (libpq)

I am having the exact same problem on a fresh install on Snow Leopard 
with Ruby 1.9.1p376 and postgres installed via homebrew. This is the 
last entry from mkmf.log

gcc -o conftest 
-I/Users/tel/.rvm/rubies/ruby-1.9.1-p376/include/ruby-1.9.1/i386-darwin10.2.0 
-I/Users/tel/.rvm/rubies/ruby-1.9.1-p376/include/ruby-1.9.1/ruby/backward 
-I/Users/tel/.rvm/rubies/ruby-1.9.1-p376/include/ruby-1.9.1 -I. 
-D_XOPEN_SOURCE -D_DARWIN_C_SOURCE 
-I/usr/local/homebrew/Cellar/postgresql/8.4.2/include  -O2 -g -Wall 
-Wno-parentheses -pipe -fno-common -arch i386 conftest.c  -L. 
-L/Users/tel/.rvm/rubies/ruby-1.9.1-p376/lib -L. 
-L/usr/local/homebrew/Cellar/postgresql/8.4.2/lib -arch i386 
-lruby-static -lms/libpq  -lpthread -ldl -lobjc  "
conftest.c: In function ‘t’:
conftest.c:5: warning: implicit declaration of function ‘PQconnectdb’
ld: library not found for -lms/libpq
collect2: ld returned 1 exit status
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: /*top*/
4: int main() {return 0;}
5: int t() { PQconnectdb(); return 0; }
/* end */

Tor Erik
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