Now that you have an idea how to form embedded SQL C programs, you probably want to know how to compile them. Before compiling you run the file through the embedded SQL C preprocessor, which converts the SQL statements you used to special function calls. After compiling, you must link with a special library that contains the needed functions. These functions fetch information from the arguments, perform the SQL command using the libpq interface, and put the result in the arguments specified for output.
The preprocessor program is called ecpg
and is
included in a normal PostgreSQL installation.
Embedded SQL programs are typically named with an extension
.pgc
. If you have a program file called
prog1.pgc
, you can preprocess it by simply
calling
ecpg prog1.pgc
This will create a file called prog1.c
. If
your input files do not follow the suggested naming pattern, you
can specify the output file explicitly using the
-o
option.
The preprocessed file can be compiled normally, for example:
cc -c prog1.c
The generated C source files include header files from the
PostgreSQL installation, so if you installed
PostgreSQL in a location that is not searched by
default, you have to add an option such as
-I/usr/local/pgsql/include
to the compilation
command line.
To link an embedded SQL program, you need to include the
libecpg
library, like so:
cc -o myprog prog1.o prog2.o ... -lecpg
Again, you might have to add an option like
-L/usr/local/pgsql/lib
to that command line.
If you manage the build process of a larger project using make, it may be convenient to include the following implicit rule to your makefiles:
ECPG = ecpg %.c: %.pgc $(ECPG) $<
The complete syntax of the ecpg
command is
detailed in ecpg.
The ecpg library is thread-safe if it is built
using the --enable-thread-safety
command-line option to
configure
. (You might need to use other threading
command-line options to compile your client code.)