libpq is the C application programmer's interface to PostgreSQL.
libpq is a set of library routines that allow client programs to
pass queries to the PostgreSQL backend server and to receive the
results of these queries. libpq is also the underlying engine
for several other PostgreSQL application interfaces, including
libpq++ (C++), libpgtcl (Tcl), Perl, and ecpg. So some aspects
of libpq's behavior will be important to you if you use one of
those packages. Three short programs are included at the end of
this section to show how to write programs that use libpq. There
are several complete examples of libpq applications in the
following directories: Frontend programs that use libpq must
include the header file libpq-fe.h and must link with the libpq
library.