Q

Precompilers explained

What is an Oracle precompiler? Is it similar to Pro*C?

It is more correct to say that Pro*C is one of Oracle's precompilers. There used to be many more precompilers in existence (and some may still persist). For instance, there was once a Pro*Fortran precompiler.

Precompilers basically work like this... There is no native SQL methods for a language like C or C++. So I could use special commands in my C program to connect to the database and issue SQL queries. For instance, to connect to the database, I'd add the following line to my C program:

   EXEC SQL CONNECT :username IDENTIFIED BY :password;
The ':username' and ':password' directives are variable placeholders. The following line shows how to put an INSERT statement into your C program:
   EXEC SQL INSERT INTO pay1 VALUES (:emp_name,
:salary);
Now it should be obvious that these two commands will cause a syntax error in your C program. So compiling this program would be fruitless. Before we compile the program, we have to "Pre-Compile" the program. This is done by envoking the 'proc' utility against our source code. This utility basically changes all of the EXEC SQL statements in our C program with valid C statements using Pro*C's libraries. Once this is done, the precompiled program is then compiled.

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This was first published in March 2002

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