Chapter 28. ECPG - Embedded SQL in C

Table of Contents

28.1. Introduction

28.2. ECPG Concepts

28.2.1. Preprocessor
28.2.2. Library

28.3. ecpg Command

28.3.1. Name
28.3.2. Synopsis
28.3.3. Options
28.3.4. Notes

28.4. Installation

28.4.1. Supported Platforms
28.4.2. Prerequisites

28.5. Embedded SQL Commands

28.5.1. Connecting to the Database Server
28.5.2. Closing a Connection
28.5.3. Running SQL Commands
28.5.4. Choosing a Connection
28.5.5. Using Host Variables
28.5.6. Using SQL Descriptor Areas
28.5.7. Usage and Examples
28.5.8. Running Programs Using ECPG
28.5.9. Error Handling Using ECPG

28.1. Introduction

Embedded SQL in C (ECPG) is a program written in C with parts of the program written in SQL.Variables used in SQL statements and SQL commands are written in specially marked sections of the C program. To build the program, the source code is first passed through an embedded SQL preprocessor which converts it to an ordinary C program, and then it is processed by a C compiler. The embedded SQL C preprocessor converts the SQL statements that were used in the program to function calls with the variables used as arguments.

At link time, the C object module is linked to a library that contains the functions used in the program. These functions fetch the information from the arguments, perform the SQL query using the ordinary interface (libpq) and put back the result in the arguments dedicated for the output.

As stated, programs written for the embedded SQL interface are normal C programs with special code inserted to perform database-related actions. This special code always has the form:

EXEC SQL ...;

The embedded SQL statements syntactically take the place of a C statement. Depending on the particular statement, they may appear at the global level or within a function. Embedded SQL statements follow the case-sensitivity rules of normal SQL code, and not those of C.