postgresql/doc/src/sgml/ecpg.sgml

<Chapter Id="ecpg">
<DocInfo>
<AuthorGroup>
<Author>
<FirstName>Linus</FirstName>
<Surname>Tolke</Surname>
</Author>
<Author>
<FirstName>Michael</FirstName>
<Surname>Meskes</Surname>
</Author>
</AuthorGroup>
<Copyright>
<Year>1996-1997</Year>
<Holder>Linus Tolke</Holder>
</Copyright>
<Copyright>
<Year>1998</Year>
<Holder>Michael Meskes</Holder>
</Copyright>
<Date>Transcribed 1998-02-12</Date>
</DocInfo>

<Title><Application>ecpg</Application> - Embedded <Acronym>SQL</Acronym> 
in <Acronym>C</Acronym></Title>

<Para>
This describes an embedded <Acronym>SQL</Acronym> in <Acronym>C</Acronym> 
package for <ProductName>Postgres</ProductName>.

It is written by <ULink url="mailto:linus@epact.se">Linus Tolke</ULink>
and <ULink url="mailto:meskes@postgresql.org">Michael Meskes</ULink>.

<Note>
<Para>
Permission is granted to copy and use in the same way as you are allowed
to copy and use the rest of the <ProductName>PostgreSQL</ProductName>.
</Para>
</Note>
</para>
<Sect1>
<Title>Why Embedded <Acronym>SQL</Acronym>?</Title>

<Para>
Embedded <Acronym>SQL</Acronym> has some small advantages over other ways 
to handle <Acronym>SQL</Acronym>
queries. It takes care of all the tedious moving of information to and
from variables in your <Acronym>C</Acronym> program. 
Many <Acronym>RDBMS</Acronym> packages
support this embedded language.
</Para>

<Para> There is an ANSI-standard describing how the embedded language should
work. <Application>ecpg</Application> was designed to meet this standard 
as much as possible. So it is
possible to port programs with embedded <Acronym>SQL</Acronym> written for
other <Acronym>RDBMS</Acronym> packages to
<ProductName>Postgres</ProductName> and thus promoting the spirit of free
software.
</Para>
</sect1>
<Sect1>
<Title>The Concept</Title>

<Para>
You write your program in <Acronym>C</Acronym> with some 
special <Acronym>SQL</Acronym> things.
For declaring variables that can be used in 
<Acronym>SQL</Acronym> statements you need to
put them in a special declare section.
You use a special syntax for the <Acronym>SQL</Acronym> queries.
</Para>

<Para>
Before compiling you run the file through 
the embedded <Acronym>SQL</Acronym> <Acronym>C</Acronym>
preprocessor and it converts the <Acronym>SQL</Acronym> statements you used 
to function
calls with the variables used as arguments. Both variables that are used
as input to the <Acronym>SQL</Acronym> statements and variables that will 
contain the
result are passed.
</Para>

<Para>
Then you compile and at link time you link with a special library that
contains the functions used. These functions (actually it is mostly one
single function) fetches the information from the arguments, performs
the <Acronym>SQL</Acronym> query using the ordinary interface 
(<FileName>libpq</FileName>) and puts back
the result in the arguments dedicated for output.
</Para>

<Para>
Then you run your program and when the control arrives to 
the <Acronym>SQL</Acronym>
statement the <Acronym>SQL</Acronym> statement is performed against 
the database and you
can continue with the result.
</Para>
</sect1>

<Sect1>
<Title>How To Use <Application>egpc</Application></Title>

<Para>
This section describes how to use the <Application>egpc</Application> tool.
</Para>

<Sect2>
<Title>Preprocessor</title>

<Para>
The preprocessor is called <Application>ecpg</Application>. 
After installation it resides in
the <ProductName>Postgres</ProductName> <FileName>bin/</FileName> directory. 
</Para>
</sect2>
<Sect2>
<Title>Library</title>

<Para>
The <Application>ecpg</Application> library is called 
<FileName>libecpg.a</FileName> or
<FileName>libecpg.so</FileName>. Additionally, the library
uses the <FileName>libpq</FileName> library for communication to the 
<ProductName>Postgres</ProductName> server so you will
have to link your program with <Parameter>-lecpg -lpq</Parameter>.
</Para>

<Para>
The library has some methods that are "hidden" but that could prove very
useful sometime.

<itemizedlist>
<listitem>
<para>
<function>ECPGdebug(int <replaceable class="parameter">on</replaceable>, FILE *<replaceable class="parameter">stream</replaceable>)</function>
turns on debug logging if called with the first argument non-zero.
Debug logging is done on <replaceable class="parameter">stream</replaceable>.
 Most <Acronym>SQL</Acronym> statement logs its arguments and result.
</Para>

<Para>
The most important one (<Function>ECPGdo</Function>) 
that is called on almost all <Acronym>SQL</Acronym>
statements logs both its expanded string,
 i.e. the string
with all the input variables inserted, and the result from the
<ProductName>Postgres</ProductName> server.
 This can be very useful when searching for errors
in your <Acronym>SQL</Acronym> statements.
</Para>
</ListItem>

<listitem>
<para>
<function>ECPGstatus()</function>
This method returns TRUE if we are connected to a database and FALSE if not.
</Para>
</ListItem>
</itemizedlist>
</Para>
</sect2>

<Sect2>
<Title>Error handling</title>

<Para>
To be able to detect errors from the <ProductName>Postgres</ProductName> 
server you include a line like
<ProgramListing>
exec sql include sqlca;
</ProgramListing>
in the include section of your file. This will define a struct and a
variable with the name <Parameter>sqlca</Parameter> as following:
<ProgramListing>
struct sqlca
{
 char sqlcaid[8];
 long sqlabc;
 long sqlcode;
 struct
 {
  int sqlerrml;
  char sqlerrmc[70];
 } sqlerrm;
 char sqlerrp[8];
 long sqlerrd[6];
 /* 0: empty                                         */
 /* 1: OID of processed tuple if applicable          */
 /* 2: number of rows processed in an INSERT, UPDATE */
 /*    or DELETE statement                           */
 /* 3: empty                                         */
 /* 4: empty                                         */
 /* 5: empty                                         */
 char sqlwarn[8];
 /* 0: set to 'W' if at least one other is 'W'       */
 /* 1: if 'W' at least one character string	     */
 /*    value was truncated when it was               */
 /*    stored into a host variable.                  */
 /* 2: empty                                         */
 /* 3: empty                                         */
 /* 4: empty                                         */
 /* 5: empty                                         */
 /* 6: empty                                         */
 /* 7: empty                                         */
 char sqlext[8];
} sqlca;
</ProgramListing>
</Para>

<Para>
If an error occured in the last <Acronym>SQL</Acronym> statement 
then <Parameter>sqlca.sqlcode</Parameter>
will be non-zero. If <Parameter>sqlca.sqlcode</Parameter> is less that 0
 then this is
some kind of serious error, like the database definition does not match
the query given. If it is bigger than 0 then this is a normal error like
the table did not contain the requested row.
</Para>

<Para>
sqlca.sqlerrm.sqlerrmc will contain a string that describes the error.
The string ends with the line number
in the source file.
</Para>

<Para>
List of errors that can occur:

<VariableList>
<VarListEntry>
<Term>-12, Out of memory in line %d.</Term>
<ListItem>
<Para>
Does not normally occur. This is a sign that your virtual memory is
exhausted.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-200, Unsupported type %s on line %d.</Term>
<ListItem>
<Para>
Does not normally occur. This is a sign that the preprocessor has
generated something that the library does not know about. Perhaps you
are running incompatible versions of the preprocessor and the library.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-201, Too many arguments line %d.</Term>
<ListItem>
<Para>
This means that <ProductName>Postgres</ProductName> has returned more
arguments than we have
matching variables. Perhaps you have forgotten a couple of the host
variables in the <Command>INTO :var1,:var2</Command>-list.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-202, Too few arguments line %d.</Term>
<ListItem>
<Para>
This means that <ProductName>Postgres</ProductName> has returned fewer
arguments than we have
host variables. Perhaps you have too many host variables in the 
<Command>INTO :var1,:var2</Command>-list.
</Para> 
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-203, Too many matches line %d.</Term>
<ListItem>
<Para>
This means that the query has returned several lines but the
variables specified are no arrays. The <Command>SELECT</Command> you made
probably was not unique.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-204, Not correctly formatted int type: %s line %d.</Term>
<ListItem>
<Para>
This means that the host variable is of an <Type>int</Type> type and the field
in the <ProductName>Postgres</ProductName> database is of another type and 
contains a value that cannot be interpreted as an <Type>int</Type>. 
The library uses <Function>strtol</Function>
for this conversion.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-205, Not correctly formatted unsigned type: %s line %d.</Term>
<ListItem>
<Para>
This means that the host variable is of an <Type>unsigned int</Type> type and
the field in the <ProductName>Postgres</ProductName> database is of another 
type and contains a
value that cannot be interpreted as an <Type>unsigned int</Type>. The library
uses <Function>strtoul</Function> for this conversion.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-206, Not correctly formatted floating point type: %s line %d.</Term>
<ListItem>
<Para>
This means that the host variable is of a <Type>float</Type> type and
the field in the <ProductName>Postgres</ProductName> database is of another 
type and contains a
value that cannot be interpreted as an <Type>float</Type>. The library
uses <Function>strtod</Function> for this conversion.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-207, Unable to convert %s to bool on line %d.</Term>
<ListItem>
<Para>
This means that the host variable is of a <Type>bool</Type> type and
the field in the <ProductName>Postgres</ProductName> database is neither 't'
nor 'f'.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-208, Empty query line %d.</Term>
<ListItem>
<Para>
<ProductName>Postgres</ProductName> returned PGRES_EMPTY_QUERY, probably
because the query indeed was empty.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-220, No such connection %s in line %d.</Term>
<ListItem>
<Para>
The program tries to access a connection that does not exist.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-221, Not connected in line %d.</Term>
<ListItem>
<Para>
The program tries to access a connection that does exist but is not open.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-230, Invalid statement name %s in line %d.</Term>
<ListItem>
<Para>
The statement you are trying to use has not been prepared.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-400, Postgres error: %s line %d.</Term>
<ListItem>
<Para>
Some <ProductName>Postgres</ProductName> error. 
The message contains the error message from the
<ProductName>Postgres</ProductName> backend.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-401, Error in transaction processing line %d. </Term>
<ListItem>
<Para>
<ProductName>Postgres</ProductName> signalled to us that we cannot start,
commit or rollback the transaction.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>-402, connect: could not open database %s.</Term>
<ListItem>
<Para>
The connect to the database did not work.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>100, Data not found line %d.</Term>
<ListItem>
<Para>
This is a "normal" error that tells you that what you are quering cannot
be found or we have gone through the cursor.
</Para>
</ListItem>
</VarListEntry>

</VariableList>
</Para>
</Sect2>
</sect1>

<Sect1>
<Title>Limitations</Title>

<Para>
What will never be included and why or what cannot be done with this
concept.

<VariableList>
<VarListEntry>
<Term>oracles single tasking possibility</Term>
<ListItem>
<Para>
Oracle version 7.0 on AIX 3 uses the OS-supported locks on the shared
memory segments and allows the application designer to link an
application in a so called single tasking way. Instead of starting one
client process per application process both the database part and the
application part is run in the same process. In later versions of oracle
this is no longer supported.
</Para>

<Para>
This would require a total redesign of the <ProductName>Postgres</ProductName> access model and
that effort can not justify the performance gained.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</Para>
</sect1>

<Sect1>
<Title>Porting From Other <Acronym>RDBMS</Acronym> Packages</Title>

<Para>
The design of <Application>ecpg</Application> follows SQL standard. So
porting from a standard RDBMS should not be a problem. Unfortunately there
is no such thing as a standard RDBMS. So <Application>ecpg</Application>
also tries to understand syntax additions as long as they do not create
conflicts with the standard. 
</Para>

<Para>
The following list shows all the known incompatibilities. If you find one
not listed please notify <ULink url="mailto:meskes@postgresql.org">Michael
Meskes</ULink>. Note, however, that we list only incompatibilities from
a precompiler of another RDBMS to <Application>ecpg</Application> and not
additional <Application>ecpg</Application> features that these RDBMS do not
have.
</Para>

<Para>
<VariableList>
<VarListEntry>
<Term>Syntax of FETCH command</Term>
<ListItem>
<Para>
The standard syntax of the FETCH command is:
</para>
<Para>
FETCH [direction] [amount] IN|FROM <Replaceable>cursor name</Replaceable>.
</Para>
<para>
<Application>ORACLE</Application>, however, does not use the keywords IN
resp. FROM. This feature cannot be added since it would create parsing
conflicts.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</Para>
</sect1>

<Sect1>
<Title>Installation</Title>

<Para>
Since version 0.5 <Application>ecpg</Application> is distributed 
together with <ProductName>Postgres</ProductName>. So you
should get your precompiler, libraries and header files compiled and
installed by default as a part of your installation.
</Para>
</sect1>

<Sect1>
<Title>For the Developer</Title>

<Para>
This section is for those who want to develop the 
<Application>ecpg</Application> interface. It
describes how the things work. The ambition is to make this section
contain things for those that want to have a look inside and the section
on How to use it should be enough for all normal questions.

So, read this before looking at the internals of the 
<Application>ecpg</Application>. If
you are not interested in how it really works, skip this section.
</Para>

<Sect2>
<Title>ToDo List</Title>

<Para>
This version the preprocessor has some flaws:

<VariableList>
<VarListEntry>
<Term>Library functions</Term>
<ListItem>
<Para>
to_date et al. do not exists. But then <ProductName>Postgres</ProductName>
has some good conversion routines itself. So you probably won't miss these.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Structures ans unions</Term>
<ListItem>
<Para>
Structures and unions have to be defined in the declare section.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Missing statements</Term>
<ListItem>
<Para>
The following statements are not implemented thus far:
<VariableList>
<VarListEntry>
<Term> exec sql allocate</Term>
<ListItem>
<Para>
</Para>
</listitem>
</VarListEntry>
<VarListEntry>
<Term> exec sql deallocate</Term>
<ListItem>
<Para>
</Para>
</listitem>
</VarListEntry>
<VarListEntry>
<Term> SQLSTATE</Term>
<ListItem>
<Para>
</Para>
</listitem>
</VarListEntry>
</VariableList>
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>message 'no data found'</Term>
<ListItem>
<Para>
The error message for "no data" in an exec sql insert select from statement
has to be 100.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>sqlwarn[6]</Term>
<ListItem>
<Para>
sqlwarn[6] should be 'W' if the PRECISION or SCALE value specified in a SET
DESCRIPTOR statement will be ignored.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</Para>
</sect2>

<Sect2>
<Title>The Preprocessor</Title>

<Para>
The first four lines written to the output are constant additions by ecpg.
These are two comments and two include lines necessary for the interface to the
library.
</Para>

<Para>
Then the preprocessor works in one pass only, reading the input file and
writing to the output as it goes along. Normally it just echoes
everything to the output without looking at it further.
</Para>

<Para>
When it comes to an <Command>EXEC SQL</Command> statements it intervenes and
changes them depending on what it is. 
The <Command>EXEC SQL</Command> statement can be one of these:

<VariableList>
<VarListEntry>
<Term>Declare sections</Term>
<ListItem>
<Para>
Declare sections begins with
<ProgramListing>
exec sql begin declare section;
</ProgramListing>
and ends with
<ProgramListing>
exec sql end declare section;
</ProgramListing>
In the section only variable declarations are allowed. Every variable
declare within this section is also entered in a list of variables
indexed on their name together with the corresponding type.
</Para>

<Para>
In particular the definition of a structure or union also has to be listed
inside a declare section. Otherwise <Application>ecpg</Application> cannot
handle these types since it simply does not know the definition.
</Para>

<Para>
The declaration is echoed to the file to make the variable a normal
C-variable also.
</Para>

<Para>
The special types VARCHAR and VARCHAR2 are converted into a named struct
for every variable. A declaration like:
<ProgramListing>
VARCHAR var[180];
</ProgramListing>
is converted into
<ProgramListing>
struct varchar_var { int len; char arr[180]; } var;
</ProgramListing>
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Include statements</Term>
<ListItem>
<Para>
An include statement looks like:
<ProgramListing>
exec sql include filename;
</ProgramListing>
Not that this is NOT the same as
<ProgramListing>
#include &lt;filename.h&gt;
</ProgramListing>
</Para>

<Para>
Instead the file specified is parsed by <Application>ecpg</Application>
itself. So the contents of the specified file is included in the resulting C
code. This way you are able to specify EXEC SQL commands in an include file.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Connect statement</Term>
<ListItem>
<Para>
A connect statement looks like:
<ProgramListing>
exec sql connect to <Replaceable>connection target</Replaceable>;
</ProgramListing>
It creates a connection to the specified database.
</Para>

<Para>
The <Replaceable>connection target</Replaceable> can be specified in the
following ways:
<VariableList>
<VarListEntry>
<Term>dbname[@server][:port][as <Replaceable>connection name</Replaceable>][user <Replaceable>user name</Replaceable>]</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term>tcp:postgresql://server[:port][/dbname][as <Replaceable>connection name</Replaceable>][user <Replaceable>user name</Replaceable>]</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term>unix:postgresql://server[:port][/dbname][as <Replaceable>connection name</Replaceable>][user <Replaceable>user name</Replaceable>]</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term><Replaceable>character variable</Replaceable>[as <Replaceable>connection name</Replaceable>][user <Replaceable>user name</Replaceable>]</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term><Replaceable>character string</Replaceable>[as <Replaceable>connection name</Replaceable>][<Replaceable>user</Replaceable>]</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term>default</Term>
<listitem><para></para></listitem>
</VarListEntry>

<VarListEntry>
<Term>user</Term>
<listitem><para></para></listitem>
</VarListEntry>
</VariableList>
</Para>

<Para>
There are also different ways to specify the user name:
<VariableList>
<VarListEntry>
<Term><Replaceable>userid</Replaceable></Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term><Replaceable>userid</Replaceable>/<Replaceable>password</Replaceable></Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term><Replaceable>userid</Replaceable> identified by <Replaceable>password</Replaceable></Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term><Replaceable>userid</Replaceable> using <Replaceable>password</Replaceable></Term>
<listitem><para></para></listitem>
</VarListEntry>
</VariableList>
</Para>

<Para> Finally the userid and the password. Each may be a constant text, a
character variable or a chararcter string.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Disconnect statements</Term>
<ListItem>
<Para>
A disconnect statement looks loke:
<ProgramListing>
exec sql disconnect [<Replaceable>connection target</Replaceable>];
</ProgramListing>
It closes the connection to the specified database.
</Para>

<Para>
The <Replaceable>connection target</Replaceable> can be specified in the
following ways:
<VariableList>
<VarListEntry>
<Term><Replaceable>connection name</Replaceable></Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term>default</Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term>current</Term>
<listitem><para></para></listitem>
</VarListEntry>
<VarListEntry>
<Term>all</Term>
<listitem><para></para></listitem>
</VarListEntry>
</VariableList>
</Para>
</ListItem>
</VarListEntry>

<!--WARNING: FROM HERE ON THE TEXT IS OUTDATED!-->
<VarListEntry>
<Term>Open cursor statement</Term>
<ListItem>
<Para>
An open cursor statement looks like:
<ProgramListing>
exec sql open <Replaceable>cursor</Replaceable>;
</ProgramListing>
and is ignore and not copied from the output.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Commit statement</Term>
<ListItem>
<Para>
A commit statement looks like
<ProgramListing>
exec sql commit;
</ProgramListing>
and is translated on the output to
<ProgramListing>
ECPGcommit(__LINE__);
</ProgramListing>
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Rollback statement</Term>
<ListItem>
<Para>
A rollback statement looks like
<ProgramListing>
exec sql rollback;
</ProgramListing>
and is translated on the output to
<ProgramListing>
ECPGrollback(__LINE__);
</ProgramListing>
</Para>
</ListItem>
</VarListEntry>

<!--STARTING HERE IT IS OKAY AGAIN!-->
<VarListEntry>
<Term>Other statements</Term>
<ListItem>
<Para>
Other <Acronym>SQL</Acronym> statements are other statements that start with 
<Command>exec sql</Command> and ends with <Command>;</Command>. 
Everything inbetween is treated
as an <Acronym>SQL</Acronym> statement and parsed for variable substitution.
</Para>

<Para>
Variable substitution occur when a symbol starts with a colon
(<Command>:</Command>). Then a variable with that name is looked for among
the variables that were previously declared within a declare section and
depending on the variable being for input or output the pointers to the
variables are written to the output to allow for access by the function.
</Para>

<Para>
For every variable that is part of the <Acronym>SQL</Acronym> request 
the function gets another ten arguments:

<SimpleList>
<Member>The type as a special symbol.</Member>
<Member>A pointer to the value or a pointer to the pointer.</Member>
<Member>The size of the variable if it is a char or varchar.</Member>
<Member>Number of elements in the array (for array fetches).</Member>
<Member>The offset to the next element in the array (for array fetches)</Member>
<Member>The type of the indicator variable as a special symbol.</Member>
<Member>A pointer to the value of the indicator variable or a pointer to the pointer of the indicator variable.</Member>
<Member>0.</Member>
<Member>Number of elements in the indicator array (for array fetches).</Member>
<Member>The offset to the next element in the indicator array (for array fetches)</Member>
</SimpleList>
</Para>

</ListItem>
</VarListEntry>
</VariableList>
</Para>
</Sect2>

<Sect2>
<Title>A Complete Example</Title>

<Para>
Here is a complete example describing the output of the preprocessor of a
file foo.pgc:
<ProgramListing>
exec sql begin declare section;
int index;
int result;
exec sql end declare section;
...
exec sql select res into :result from mytable where index = :index;
</ProgramListing>
is translated into:
<ProgramListing>
/* Processed by ecpg (2.6.0) */
/* These two include files are added by the preprocessor */
#include &lt;ecpgtype.h&gt;;
#include &lt;ecpglib.h&gt;;

/* exec sql begin declare section */

#line 1 "foo.pgc"

 int index;
 int result;
/* exec sql end declare section */
...
ECPGdo(__LINE__, NULL, "select  res  from mytable where index = ?     ",
	ECPGt_int,&amp;(index),1L,1L,sizeof(int),
        ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT,
        ECPGt_int,&amp;(result),1L,1L,sizeof(int),
        ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
#line 147 "foo.pgc"

</ProgramListing>
(the indentation in this manual is added for readability and not
something that the preprocessor can do.)
</Para>
</sect2>

<Sect2>
<Title>The Library</Title>

<Para>
The most important function in the library is the <Function>ECPGdo</Function>
function. It takes a variable amount of arguments. Hopefully we will not run
into machines with limits on the amount of variables that can be
accepted by a vararg function. This could easily add up to 50 or so
arguments.
</Para>

<Para>
The arguments are:

<VariableList>
<VarListEntry>
<Term>A line number</Term>
<ListItem>
<Para>
This is a line number for the original line used in error messages only.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>A string</Term>
<ListItem>
<Para>
This is the <Acronym>SQL</Acronym> request that is to be issued. 
This request is modified
by the input variables, i.e. the variables that where not known at
compile time but are to be entered in the request. Where the variables
should go the string contains <Quote>;</Quote>.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Input variables</Term>
<ListItem>
<Para>
As described in the section about the preprocessor every input variable
gets ten arguments.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>ECPGt_EOIT</Term>
<ListItem>
<Para>
An enum telling that there are no more input variables.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>Output variables</Term>
<ListItem>
<Para>
As described in the section about the preprocessor every input variable
gets ten arguments. These variables are filled by the function.
</Para>
</ListItem>
</VarListEntry>

<VarListEntry>
<Term>ECPGt_EORT</Term>
<ListItem>
<Para>
An enum telling that there are no more variables.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</Para>

<Para>
All the <Acronym>SQL</Acronym> statements are performed in one transaction
unless you issue a commit transaction. To get this auto-transaction going
the first statement or the first after statement after a commit or rollback
always begins a transaction. To disable this feature per default use the
'-t' option on the commandline
</Para>

<Para>
To be completed: entries describing the other entries.
</Para>
</sect2>
</sect1>
</Chapter>