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.