ECPG(1) PostgreSQL Client Applications ECPG(1)NAMEecpg - Embedded SQL C preprocessor
SYNOPSISecpg [ -v ] [ -t ] [ -I include-path ] [ -o outfile ] file1 [ file2 ] [ ... ]
INPUTS
ecpg accepts the following command line arguments:
-v Print version information.
-t Turn off auto-transaction mode.
-I path
Specify an additional include path. Defaults are .,
/usr/local/include, the Postgres include path which is defined
at compile time (default: /usr/local/pgsql/lib), and
/usr/include.
-o Specifies that ecpg should write all its output to outfile. If
no such option is given the output is written to name.c, assum‐
ing the input file was named name.pgc. If the input file does
have the expected .pgc suffix, then the output file will have
.pgc appended to the input file name.
file The files to be processed.
OUTPUTS
ecpg will create a file or write to stdout.
return value
ecpg returns 0 to the shell on successful completion, -1 for
errors.
DESCRIPTIONecpg is an embedded SQL preprocessor for the C language and the Post‐
gres. It enables development of C programs with embedded SQL code.
Linus Tolke (<linus@epact.se>) was the original author of ecpg (up to
version 0.2). Michael Meskes (<meskes@debian.org>) is the current
author and maintainer of ecpg. Thomas Good (<tomg@q8.nrnet.org>) is
the author of the last revision of the ecpg man page, on which this
document is based.
USAGE
PREPROCESSING FOR COMPILATION
An embedded SQL source file must be preprocessed before compilation:
ecpg [ -d ] [ -o file ] file.pgc
where the optional -d flag turns on debugging. The .pgc extension is
an arbitrary means of denoting ecpg source.
You may want to redirect the preprocessor output to a log file.
COMPILING AND LINKING
Assuming the Postgres binaries are in /usr/local/pgsql, you will need
to compile and link your preprocessed source file:
gcc -g -I /usr/local/pgsql/include [ -o file ] file.c -L /usr/local/pgsql/lib -lecpg -lpq
GRAMMAR
LIBRARIES
The preprocessor will prepend two directives to the source:
#include <ecpgtype.h>
#include <ecpglib.h>
VARIABLE DECLARATION
Variables declared within ecpg source code must be prepended with:
EXEC SQL BEGIN DECLARE SECTION;
Similarly, variable declaration sections must terminate with:
EXEC SQL END DECLARE SECTION;
Note: Prior to version 2.1.0, each variable had to be declared
on a separate line. As of version 2.1.0 multiple variables may
be declared on a single line:
char foo(16), bar(16);
ERROR HANDLING
The SQL communication area is defined with:
EXEC SQL INCLUDE sqlca;
Note: The sqlca is in lowercase. While SQL convention may be
followed, i.e., using uppercase to separate embedded SQL from C
statements, sqlca (which includes the sqlca.h header file) MUST
be lowercase. This is because the EXEC SQL prefix indicates that
this INCLUDE will be parsed by ecpg. ecpg observes case sensi‐
tivity (SQLCA.h will not be found). EXEC SQL INCLUDE can be
used to include other header files as long as case sensitivity
is observed.
The sqlprint command is used with the EXEC SQL WHENEVER statement to
turn on error handling throughout the program:
EXEC SQL WHENEVER sqlerror sqlprint;
and
EXEC SQL WHENEVER not found sqlprint;
Note: This is not an exhaustive example of usage for the EXEC
SQL WHENEVER statement. Further examples of usage may be found
in SQL manuals (e.g., `The LAN TIMES Guide to SQL' by Groff and
Weinberg).
CONNECTING TO THE DATABASE SERVER
One connects to a database using the following:
EXEC SQL CONNECT TO dbname;
where the database name is not quoted. Prior to version 2.1.0, the
database name was required to be inside single quotes.
Specifying a server and port name in the connect statement is also pos‐
sible. The syntax is:
dbname[@server][:port]
or
<tcp|unix>:postgresql://server[:port][/dbname][?options]
QUERIES
In general, SQL queries acceptable to other applications such as psql
can be embedded into your C code. Here are some examples of how to do
that.
Create Table:
EXEC SQL CREATE TABLE foo (number int4, ascii char(16));
EXEC SQL CREATE UNIQUE index num1 on foo(number);
EXEC SQL COMMIT;
Insert:
EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
EXEC SQL COMMIT;
Delete:
EXEC SQL DELETE FROM foo WHERE number = 9999;
EXEC SQL COMMIT;
Singleton Select:
EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad';
Select using Cursors:
EXEC SQL DECLARE foo_bar CURSOR FOR
SELECT number, ascii FROM foo
ORDER BY ascii;
EXEC SQL FETCH foo_bar INTO :FooBar, DooDad;
EXEC SQL CLOSE foo_bar;
EXEC SQL COMMIT;
Updates:
EXEC SQL UPDATE foo
SET ascii = 'foobar'
WHERE number = 9999;
EXEC SQL COMMIT;
NOTES
There is no EXEC SQL PREPARE statement.
The complete structure definition MUST be listed inside the declare
section.
See the TODO file in the source for some more missing features.
Application 29 March 2001 ECPG(1)
