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>Chapter 33. <SPAN
CLASS="APPLICATION"
>ECPG</SPAN
> - Embedded <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> in C</TD
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><A
NAME="ECPG-PROCESS"
>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) $<</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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