C++ linking error when linking postgresql

Question

When compiling my code I run into an issue as follows:

io.cpp:21: undefined reference to `PQconnectdb'

as well as all other instances of missing postgres function calls occurring in my code. Obviously this is a linking problem, I'm just not sure what the link issue is.

I'm compiling with the following:

mpiCC -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ decisioning_mpi.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ io.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ calculations.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ rules.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Instrument.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Backtest_Parameter_CPO.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Backtest_Trade_CPO.cpp
g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Data_Bar.cpp
mpiCC -o decisioning_mpi -O2 -g -Wall -Werror -L/usr/lib -lm -lpq decisioning_mpi.o 
io.o calculations.o rules.o Instrument.o Backtest_Parameter_CPO.o Backtest_Trade_CPO.o Data_Bar.o

It should be noted that this is the correct directory for libpq-fe.h and that I'm linking pq, so I'm not exactly sure why the postgres functions aren't linking correctly. I'm running Ubuntu 12.04 and installed psql (PostgreSQL) 9.1.6 from synaptic. As well I'll short circuit this, I am using #include "libpq-fe.h".

Any ideas on how I can get this linking issue resolved?

Put your libraries at the end of the final link command line. (Try a google search for "order of libraries link site:stackoverflow.com" to get quite a few related questions and answers) — Mat
– Mat, Commented Nov 17, 2012 at 11:03

billz · Accepted Answer · 2012-11-17 11:08:22Z

1

put -L/usr/lib/ -lm -lpq in the end of link command, the linker can then find the symbols

mpiCC -o decisioning_mpi -O2 -g -Wall -Werror decisioning_mpi.o io.o \
calculations.o rules.o Instrument.o Backtest_Parameter_CPO.o \
Backtest_Trade_CPO.o Data_Bar.o -L/usr/lib -lm -lpq

GCC Link Reference: http://www.network-theory.co.uk/docs/gccintro/gccintro_18.html

answered Nov 17, 2012 at 11:08

billz

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1 Comment

Brent Over a year ago

Thanks, that did it. I feel like I have egg on my face for it being the order of the linking, here I thought that I had setup postgresql incorrectly.

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