Introduction To Informix Esql C

Programming with INFORMIX-ESQL/C

What Is INFORMIX-ESQL/C?

ESQL/C is an SQL application programming interface (API) that enables you to embed Structured Query Language (SQL) statements directly into a C program. The ESQL/C preprocessor, which the esql command calls, converts each SQL statement and all Informix-specific code to C.

To access a database server through an ESQL/C application

  1. Write embedded SQL statements and calls to ESQL/C library functions into your C code to create an ESQL/C program.
  2. Convert the ESQL/C program to a C executable file with the esql command.

Compiling an ESQL/C Program: You type the esql command to compile your ESQL/C program. The esql command passes your ESQL/C source file to the ESQL/C preprocessor and to the C compiler. It passes along options that are specific to both the ESQL/C preprocessor and the C compiler to preprocess, compile, and link your ESQL/Cprogram.

The esql command follows these steps to carry out the conversion:

  • In Stage 1, the ESQL/C preprocessor performs the following steps:
    • Incorporates header files into the source file when it processes all include directives ($include and EXEC SQL include statements)
    • Creates or removes compile-time definitions when it processes all define ($define and EXEC SQL define) and undef ($undef and EXEC SQL undef) directives
    • In Stage 2, the ESQL/C preprocessor processes any conditional compilation directives (ifdef, ifndef, else, elif, endif) and translates embedded SQL statements to ESQL/C function calls and special data structures.

Stages 1 and 2 mirror the preprocessor and compiler stages of the C compiler. Successful completion of the preprocessing step yields a C source file (.c extension).

Default Compilation Order
ESQL/C source program -> ESQL/C preprocessor -> C source program with SQL statements and ESQL/C calls -> C language preprocessor and compiler -> Executable program

INFORMIX-ESQL/C Data Types

Working with Character and String Data Types

Working with the DECIMAL Data Type

Working with Numeric Data Types

Working with Time Data Types

Working with INFORMIX-Universal Server Smart Large Objects

Working with Simple Large Objects

Working with INFORMIX-Universal Server Complex Data Types

Working with INFORMIX-Universal Server Opaque Data Types

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