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.
You can use pg_config
or pkg-config
with package name libecpg
to get the paths for your
installation.
If you manage the build process of a larger project using make, it might 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 by default. However, you might need to use some threading command-line options to compile your client code.
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