What is Pro

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What is Pro*C

Pro*c is writing a C program with embedded SQL statements. It is possible to

access Oracle database from C program using Pro*C. It allows you to use the

power and flexibility of C language for data processing and SQL to retrieve and

manipulate data of Oracle database.Oracle provides PROC compiler, which takes a C program with embedded SQL

statements and converts the embedded SQL statements to Oracle Runtime Library

(also supplied by Oracle).

The compiled C program is a pure C code and can be compiled with C compiler.

Pro*C supports Microsoft Visual C++ 6.0 compiler.

The following is the overall process related to Pro*C.

• First write a C program with embedded SQL commands to perform database

operations. Save this file with the extension .PC.

•

Compile this program using PRO*C Compiler – PROC – provided byOracle. The output of Pro*C compiler is a pure C program with all

embedded SQL commands replaced with calls to C function in Oracle

runtime library. It generates a .C file.

• Compile the .C file generated by Pro*C compiler using C compiler that is

supported by Pro*C. On Microsoft platform, Visual C++ 6.0 compiler is

supported.

• The compiler generates .EXE file by linking C program with Libraries

provided by Oracle.

• Run .EXE file.

Why Pro*C?

The following are some of the reasons why use have to use PreCompiler such as

Pro*C.

• To use the power and flexibility of a highlevel langauge.

• To provide the required user interface

• To customize applications, which may not be possible with available tools.

For example, there may be a report that cannot be generated using any of the

available report writers.In such cases it is possible to use C to generate that

report by taking data from Oracle database.

• To access Oracle data on one side and a particular hardware on the other

side.

The above list is by no means complete. It is only to give you some idea about

what can be done and not a comprehensive list of all possibilities.



What You Need?

What does one need to know and have to use Pro*C.? First, we have to installPro*C software. At the time of installing Oracle, make sure you select Pro*C

components. You can check whether your installation of Oracle has Pro*C

components installed by examining PRECOMP directory of Oracle home – say

C:\ORACLE8i\PRECOMP.

The following is the structure of PRECOMP directory.

PUBLI

CContains the required header (.h) files.

LIB Contains the libraries used by languagelinker.

DEMO Contains demo program.

ADMI

NContains configuration files.

DOC Documentation related to Precompilers.

Depending on the language you want to use load appropriate compiler. The

languages supported by Precompiler is C/C++, COBOL , FORTRAN, and ADA.As we are talking about Pro*C, we need to install C/C++ compiler that is

supported by Oracle. On Windows, Oracle supports Visual C++ 6.0 compiler. So

make sure you have installed Visual C++ 6.0.

So far knowledge is concerned, you must be aware of C of course and SQL and if

required PL/SQL

Simple Pro*C Program

The best way to understand any kind of programming is to start writing a program.

So let us see how a simple Pro*C program is written, compiled and run.

The following is a simple Pro*C program to connect to Oracle using SCOTTusername and password TIGER.

Write the following code as save the file with .PC extension. The example is saved

with the name SAMPLE.PC.

#include <stdio.h>

#include <string.h>



#include <sqlda.h>

#include <sqlcpr.h>

EXEC SQL BEGIN DECLARE SECTION;

VARCHAR uid[30];

VARCHAR pwd[30];

EXEC SQL END DECLARE SECTION;

EXEC SQL INCLUDE SQLCA.H;

void main()

{

strcpy(uid.arr,"SCOTT");uid.len =strlen(uid.arr);

strcpy(pwd.arr,"TIGER");

pwd.len = strlen(pwd.arr);

EXEC SQL WHENEVER SQLERROR GOTO errexit;

EXEC SQL CONNECT :uid IDENTIFIED BY :pwd;

printf("Connected to Oracle8i using Scott/Tiger\n");

EXEC SQL COMMIT WORK RELEASE;return;

errexit:

printf("Connection failed");

return;

} /* end of main */

The following few sections will explain the above program. First we need to

include some .h files. Some of them are belonging to C and others such as

SQLDA.H SQLCPR.H are required for embedded sql. These files are present in

PUBLIC directory of PRECOMP directory.



Embedded Commands

These commands are the commands that Pro*C compiler takes care of. They are

meant for Pro*C compiler. They are either converted to some calls to runtime

library of Oracle or provide required information to Pro*C compiler. So these

command are of two types.

• Executable - they are executed by Oracle to perform some operation

• Declarative - they are used to declare host variables etc.

All embedded commands are included into C program using the prefix EXEC

SQL. That means Pro*C compiler is converting all lines that start with EXEC SQL

into appropriate C code.

Declaring variables that are to be used with SQL statements is to be done inside

BEGIN DECLARE SECTION and END DECLARE SECTION. This section is

used to declare host variables.

EXEC SQL BEGIN DECLARE SECTION;

VARCHAR uid[30];

VARCHAR pwd[30];

EXEC SQL END DECLARE SECTION;

Host Variables

Host variables are variables of the host language that are used with SQL command

in embedded sql. Host variables are used to communicate with Oracle. Host

variables are used to send values from C to Oracle and also to receive values from

Oracle.

Host variables are declared between BEGIN DECLARE SECTION and END

DECLARE SECTION and used in embedded sql with prefix : (colon).



A host variables can be associated with Indicator Variable that indicates the value

or condition of the host variable.

In the sample program we created two host variables - uid and pwd. Each of type

VARCHAR, which in internally converted to a structure with two members - arr and len.

The statement INCLUDE SQLCA.H is used to include a structure called SQLCA,

which stands for SQL Communication Area. This is used by Oracle to provide

information about the most recently executed command. We will see more on this

in later articles.

EXEC SQL INCLUDE SQLCA.H;

Using Host Variables

Then we use host variables - uid and pwd. Each of these variables contains an

array of char and an int variable. Internally uid is converted to a variable of

structure.

In order to use a host variable of VARCHAR type, we need to copy the string to

arr and length of the string to len members.

strcpy(uid.arr,"SCOTT");

uid.len =strlen(uid.arr);

strcpy(pwd.arr,"TIGER");

pwd.len = strlen(pwd.arr);

Error handling

WHENEVER statement is used to specify what action to be taken when there is an

error in the subsequent statements.



EXEC SQL WHENEVER SQLERROR GOTO errexit;

The above statement specifies if there is an error in any of the subsequent

statements then control should goto a label called errexit .

There are other forms of WHENEVER statement that we will examine in later

articles.

The next statement used CONNECT command to connect to Oracle. It uses host

variables - uid and pwd to supply username and password. Once connection is

successful then it displays a message and then COMMIT WORK RELEASE will

release the resources and log off.

EXEC SQL CONNECT :uid IDENTIFIED BY :pwd;

printf("Connected to Oracle8i using Scott/Tiger\n");

EXEC SQL COMMIT WORK RELEASE;

return;

Statements given after lable errexit will be executed when connection is not

successful. It displays an error message and terminates main().

errexit:

printf("Connection failed");



return;

Compiling

After the sample program is saved under the name SAMPLE.PC. Take the

following steps to compile and run the program.

The following steps assume that SAMPLE.PC is in C:\SRIKANTH\PROC

directory and Oracle is installed into C:\ORACLE8I directory.

Also make sure BIN directory of Oracle and BIN directory of Visual C++ are in

system PATH.

• Make C:\SRIKANTH\PROC directory the current directory.

• Use the following command to compile .PC to create .C.

• PROC SAMPLE.C

• Once SAMPLE.C file is created in the current directory then compile itusing command line compiler of VC++ as follows to create SAMPLE.EXE.

• CL /IC:\ORACLE8I\PRECOMP\PUBLIC SAMPLE.C /LINK

C:\ORACLE8i\PRECOMP\LIB\MSVC\ORASQL8.LIB

/Iis used to specify where compiler can find include files.

/LINK is used to pass information to linker. In this case we passwed name

of library to be used by the linker.

• Once SAMPLE.EXE is created, run it from command line as follows.

C:\SRIKANTh\PROC\>SAMPLE

Connected to Oracle8i using Scott/Tiger

So that's all you have to do to create a simple Pro*C program. We will see more

about Pro*C in future articles.



P.Srikanth.

Pro*C

Pro*C is a C/ C++ precompiler that lets you embed SQL calls directly into C-

code. It is a lot more efficient coding-wise than using OCI.

• Pro*C - comes bundled with the Oracle client.

• Used for doing embedded SQL programming using C programs.

• Installation includes a proc or proc.exe executable under$ORACLE_HOME /bin

• Demo programs are under $ORACLE_HOME/precomp/demo/proc[edit] Getting started on Unix

Start with this simple exercise (if you are running Unix):

• cd $ORACLE_HOME/demo/ directory, usually you find some Pro*Cprograms under $ORACLE_HOME/precomp/demo/proc/ or$ORACLE_HOME/plsql/demo/ directories, the suffix of the Pro*Cprograms are *.pc.

• Make sure that the following environment variables are set:

o

LD_LIBRARY_PATHo ORACLE_HOME

o PATH

• If you are running the following UNIX types the following environmentvariables need to be set:

o HP/UX - Set SHLIB_PATH to same value as LD_LIBRARY_PATH.

o AIX - Set LIBPATH to same value as LD_LIBRARY_PATH.

o AIX 4.3+ - Set LINK_CNTRL as L_PTHREADS_D7.

• Make sure that correct "C" Compiler version is present on your system:

o You may use "which" and "what" command, say which cc. Or use cc-v

• Relink the sample Pro*C programs:

o There is a sample make file called demo_plsql.mk, which relinks andcompiles some of the sample Pro*C programs

http://www.orafaq.com/wiki/C

http://www.orafaq.com/wiki/Precompilers

http://www.orafaq.com/wiki/SQL


http://www.orafaq.com/wiki/OCI

http://www.orafaq.com/wiki/ORACLE_HOME

http://www.orafaq.com/wiki/index.php?title=Pro*C&action=edit&section=1

http://www.orafaq.com/wiki/Unix

http://www.orafaq.com/wiki/Precompilers

http://www.orafaq.com/wiki/SQL


http://www.orafaq.com/wiki/OCI

http://www.orafaq.com/wiki/ORACLE_HOME

http://www.orafaq.com/wiki/index.php?title=Pro*C&action=edit&section=1

http://www.orafaq.com/wiki/Unix




o You can edit the file demo_plsql.mk to make necessary modificationsto the database username/password (scott/tiger found indemo_plsql.mk) .etc.

o make -f demo_plsql.mk demos

o To Relink and make a single file use, make -f demo_plsql.mk sample1or make -f demo_proc.mk build EXE=sample1 OBJS=sample1.o ormake -f demo_proc.mk build EXE=sample1 OBJS=sample1.oPROCFLAGS="sqlcheck=semantics userid=username/password

• Running "make" yields the executable files. A makefile is a description fileused by the UNIX 'make' utility. The makefile includes dependencies andrules for building a target executable. Such rules can be precompilingcommands, compiling commands, linking commands, or commands forremoving temporary files. The ultimate goal of the make utility is to buildthe final executable program using the rules contained within the makefile.

The makefile can have any name.• /*--------------------------------------------------------------------

• * Very simple example Pro*C program to select records from a database

• *

• * Frank Naude - Sep 2000

• *--------------------------------------------------------------------

• */

•

• #include <stdio.h>

• #include <sqlca.h>

•

• void sqlerror();

•

• EXEC SQL BEGIN DECLARE SECTION;

• char *connstr = "scott/tiger";



• char db_ename[30];

• int db_deptno;

• EXEC SQL END DECLARE SECTION;

•

• void main() {

• EXEC SQL WHENEVER SQLERROR DO sqlerror();

• EXEC SQL WHENEVER SQLWARNING CONTINUE;

• EXEC SQL CONNECT :connstr;

•

• EXEC SQL WHENEVER NOTFOUND GOTO notfound;

• EXEC SQL SELECT ENAME, DEPTNO

• INTO db_ename, db_deptno

• FROM EMP

• WHERE EMPNO = 7369;

•

• found:

• printf("%s is in department %i\n", db_ename, db_deptno);

• return;

•

• notfound:

• printf("Employee record not found in database.\n");

• return;

• }



•

• void sqlerror() {

• printf("Stop Error:\t%25i\n", sqlca.sqlcode);

• return;

• }

• /*--------------------------------------------------------------------

• * Very simple example Pro*C program to fetch multiple records

• * from database


• *--------------------------------------------------------------------

• */

•



•


•


• char *connstr = "scott/tiger";


• int db_deptno;


•



• void main() {




•

• EXEC SQL DECLARE emp_cursor CURSOR FOR

• SELECT ENAME, DEPTNO

• FROM EMP;

•

• EXEC SQL OPEN emp_cursor;

•

• EXEC SQL WHENEVER NOT FOUND DO break;

• for (;;) {

• EXEC SQL FETCH emp_cursor INTO :db_ename, :db_deptno;

• printf("\t%s\t%i\n", db_ename, db_deptno);

• }

•

• EXEC SQL CLOSE emp_cursor;

• EXEC SQL COMMIT WORK RELEASE;

• return;

• }

•





• EXEC SQL WHENEVER SQLERROR CONTINUE;

• EXEC SQL ROLLBACK WORK RELEASE;

• return;

• }

• /*--------------------------------------------------------------------

• * Example Pro*C program to execute a database procedure with known

• * IN OUT arguments.


• *--------------------------------------------------------------------

• */

•



•


•


• char *sqlstmt = "begin :x := upper(:x); end;";

• char *connstr = "scott/tiger@ORCL";

• char valstr[25];


•



• void main() {




•

• EXEC SQL PREPARE stmt1 FROM :sqlstmt;

• strcpy(valstr, "Hi world");

• EXEC SQL EXECUTE stmt1 USING :valstr;

•

• printf("Return value: %s\n", valstr);

• return;

• }

•


• printf("Stop Error:\t%25i\n",sqlca.sqlcode);

• return;

• }

• /*--------------------------------------------------------------------

• * Very simple example Pro*C program to connect to more than one

• * database to do work.


• *--------------------------------------------------------------------

• */



•



•


•


• char *connstr1 = "scott/tiger";

• char *connstr2 = "scott/tiger@ORCL";


• int db_deptno;


•

• void main() {



•

• /* give the database connections unique names */

• EXEC SQL DECLARE db1 DATABASE;

• EXEC SQL DECLARE db2 DATABASE;

•

• /* connect to different databases */

• EXEC SQL AT db1 CONNECT :connstr1;



• EXEC SQL AT db2 CONNECT :connstr2;

•

• EXEC SQL AT DB1 DECLARE emp_cursor CURSOR FOR

• SELECT ENAME, DEPTNO

• FROM EMP;

•

• EXEC SQL AT DB1 OPEN emp_cursor;

•

• EXEC SQL WHENEVER NOT FOUND DO break;

• for (;;) {

• EXEC SQL AT DB1 FETCH emp_cursor INTO :db_ename,

:db_deptno;

• printf("\t%s\t%i\n", db_ename, db_deptno);

• }

•

• EXEC SQL AT DB1 CLOSE emp_cursor;

•

• /* logoff from both databases */

• EXEC SQL AT DB1 COMMIT WORK RELEASE;

• EXEC SQL AT DB1 COMMIT WORK RELEASE;

• return;

• }

•






• EXEC SQL AT DB1 ROLLBACK WORK RELEASE;

• EXEC SQL AT DB2 ROLLBACK WORK RELEASE;

• return;

• }

• /*--------------------------------------------------------------------

• * Example Pro*C program to describe a database procedure and print

• * its arguments.


• *--------------------------------------------------------------------

• */

•

• #define MAX_PLSQL_PARAMETERS 30

•

• #include <stdlib.h>


•

• #define SQLCA_INIT

• EXEC SQL INCLUDE sqlca;

•

• typedef char strz[31];



• EXEC SQL TYPE strz IS STRING(31) REFERENCE;

•

• /* Declare functions */

• int ora_logon();

• int ora_logoff();

• int ora_error();

• int plsql_desc(char *procname);

•

• /*--------------------------------------------------------------------*/

• int main() {

• ora_logon();

• printf("About to describe procedure DBMS_OUTPUT.PUT_LINE...\n");

• plsql_desc("DBMS_OUTPUT.PUT_LINE");

• ora_logoff();

• return 0;

• }

•

• /*--------------------------------------------------------------------

• * Login to the Oracle database

• *--------------------------------------------------------------------*/

• int ora_logon() {

•




• char *oracleid = "monitor/monitor";


•


• EXEC SQL CONNECT :oracleid;

• if (sqlca.sqlcode != 0) {

• printf("ERROR: Unable to login to Oracle\n%.*s",

• sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc);

• }

• }

•

• /*--------------------------------------------------------------------

• * Logoff from the Oracle database

• *--------------------------------------------------------------------*/

• int ora_logoff() {


• EXEC SQL ALTER SESSION SET SQL_TRACE FALSE;

• EXEC SQL COMMIT WORK RELEASE;

• }

•

• /*--------------------------------------------------------------------

• * Handle Oracle errors

• *--------------------------------------------------------------------*/



• int ora_error() {

• char errmsg[2000];

• unsigned int buf_len, msg_len;

•


• buf_len = sizeof(errmsg);

• sqlglm(errmsg, &buf_len, &msg_len);

• printf("Oracle Error: %.*s\n", msg_len, errmsg);

• exit(8);

• }

•

• /*--------------------------------------------------------------------

• * Describe PL/SQL parameters

• *--------------------------------------------------------------------*/

• int plsql_desc(char *procname) {

•

• int overload [MAX_PLSQL_PARAMETERS];

• int position [MAX_PLSQL_PARAMETERS];

• int level [MAX_PLSQL_PARAMETERS];

• static strz argument_name [MAX_PLSQL_PARAMETERS];

• static short arg_name_ind [MAX_PLSQL_PARAMETERS];

• static int datatype [MAX_PLSQL_PARAMETERS];

• int default_value [MAX_PLSQL_PARAMETERS];



• int in_out [MAX_PLSQL_PARAMETERS];

• int length [MAX_PLSQL_PARAMETERS];

• int precision [MAX_PLSQL_PARAMETERS];

• int scale [MAX_PLSQL_PARAMETERS];

• int radix [MAX_PLSQL_PARAMETERS];

• int spare [MAX_PLSQL_PARAMETERS];

• int i = 0;

• int t = -1; /* Default return type is -1 */

•

• for (i=0; i<MAX_PLSQL_PARAMETERS; i++) {

• overload[i] = -1;

• }

•

• EXEC SQL WHENEVER SQLERROR DO ora_error();

• EXEC SQL EXECUTE

• BEGIN

• dbms_describe.describe_procedure(:procname, NULL, NULL,

• :overload, :position, :level, :argument_name:arg_name_ind,

• :datatype, :default_value, :in_out, :length, :precision,

• :scale, :radix, :spare);

• END;

• END-EXEC;

•



• /* The datatypes and their numeric type codes are:

• 0 placeholder for procedures with no arguments

• 1 VARCHAR, VARCHAR, STRING

• 2 NUMBER, INTEGER, SMALLINT, REAL, FLOAT, DECIMAL

• 3 BINARY_INTEGER, PLS_INTEGER, POSITIVE, NATURAL

• 8 LONG

• 11 ROWID

• 12 DATE

• 23 RAW

• 24 LONG RAW

• 96 CHAR (ANSI FIXED CHAR), CHARACTER

• 106 MLSLABEL

• 250 PL/SQL RECORD

•

251 PL/SQL TABLE• 252 PL/SQL BOOLEAN

• */

•

• /* Print parameters with types */

• i = 0;

• while ((overload[i] != -1) && (i < MAX_PLSQL_PARAMETERS)) {

• printf ("pos=%d overl=%d ", position[i], overload[i]);

• if (arg_name_ind[i] != -1) {

• printf("nam=%s ", argument_name[i]);



• }

• printf("lev=%d typ=%d len=%d ", level[i],datatype[i],length[i]);

• printf("prec=%d scale=%d radix=%d\n",precision[i],scale[i],radix[i]);

• i++;

• }

•

• }

•

• /* EOF*************************************************************

***/

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