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>Chapter 33. <SPAN
CLASS="APPLICATION"
>ECPG</SPAN
> - Embedded <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> in C</TD
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>33.10. Processing Embedded SQL Programs</A
></H1
><P
>   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 <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
   <ACRONYM
CLASS="ACRONYM"
>C</ACRONYM
> preprocessor, which converts the
   <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> 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 <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> command using
   the <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> interface, and put the result
   in the arguments specified for output.
  </P
><P
>   The preprocessor program is called <TT
CLASS="FILENAME"
>ecpg</TT
> and is
   included in a normal <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation.
   Embedded SQL programs are typically named with an extension
   <TT
CLASS="FILENAME"
>.pgc</TT
>.  If you have a program file called
   <TT
CLASS="FILENAME"
>prog1.pgc</TT
>, you can preprocess it by simply
   calling:
</P><PRE
CLASS="PROGRAMLISTING"
>ecpg prog1.pgc</PRE
><P>
   This will create a file called <TT
CLASS="FILENAME"
>prog1.c</TT
>.  If
   your input files do not follow the suggested naming pattern, you
   can specify the output file explicitly using the
   <TT
CLASS="OPTION"
>-o</TT
> option.
  </P
><P
>   The preprocessed file can be compiled normally, for example:
</P><PRE
CLASS="PROGRAMLISTING"
>cc -c prog1.c</PRE
><P>
   The generated C source files include header files from the
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation, so if you installed
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> in a location that is not searched by
   default, you have to add an option such as
   <TT
CLASS="LITERAL"
>-I/usr/local/pgsql/include</TT
> to the compilation
   command line.
  </P
><P
>   To link an embedded SQL program, you need to include the
   <TT
CLASS="FILENAME"
>libecpg</TT
> library, like so:
</P><PRE
CLASS="PROGRAMLISTING"
>cc -o myprog prog1.o prog2.o ... -lecpg</PRE
><P>
   Again, you might have to add an option like
   <TT
CLASS="LITERAL"
>-L/usr/local/pgsql/lib</TT
> to that command line.
  </P
><P
>   If you manage the build process of a larger project using
   <SPAN
CLASS="APPLICATION"
>make</SPAN
>, it might be convenient to include
   the following implicit rule to your makefiles:
</P><PRE
CLASS="PROGRAMLISTING"
>ECPG = ecpg

%.c: %.pgc
        $(ECPG) $&lt;</PRE
><P>
  </P
><P
>   The complete syntax of the <TT
CLASS="COMMAND"
>ecpg</TT
> command is
   detailed in <A
HREF="app-ecpg.html"
><SPAN
CLASS="APPLICATION"
>ecpg</SPAN
></A
>.
  </P
><P
>   The <SPAN
CLASS="APPLICATION"
>ecpg</SPAN
> library is thread-safe by
   default.  However, you might need to use some threading
   command-line options to compile your client code.
  </P
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