INFORMIX-ESQL/C Programmer's Manual Compiling Programs

You use 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/C program.

To preprocess, compile, and link a program that contains ESQL/C statements, you must pass it through the ESQL/C preprocessor. You use the esql command to run the preprocessor on your ESQL/C source file and create an executable file. The esql command follows these steps to carry out the conversion:

• In stage one, 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 two, 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 one and two mirror the preprocessor and compiler stages of the C compiler. Successful completion of the preprocessing step yields a C source file (.c extension). For information about command-line options that affect the preprocessing step, see Options That Affect Preprocessing.

The esql command processor is installed as part of the ESQL/C product. Before you use esql, make sure that:

• the filename of the ESQL/C source file has the .ec or the .ecp.
• the INFORMIXDIR and PATH environment variables are set correctly.

For information on how to set the INFORMIXDIR and PATH variables, see the Client Products Installation Guide for your operating system.

For a detailed explanation of the syntax of the esql command, see Using the esql Command.

Warning: Always link your ESQL/C program with the esql program. The lists of libraries that Informix uses can change between releases. Linking with esql assures that your ESQL/C program will link correctly with Informix libraries.

The C code that the ESQL/C preprocessor generates might change from one release of the product to the next. Therefore, do not design ESQL/C programs that depend on how Informix implements the functionality and features of the product in the C code that the ESQL/C preprocessor generates. Instead, develop your programs with the functionality and features of the product that this manual describes.

C Preprocessor and Compiler

The esql command does not itself compile and link the ESQL/C program. The esql command translates ESQL/C code to C code and then calls the C compiler to compile and link the C code. The C preprocessor preprocesses the C language preprocessing directives. The C compiler performs the compilation, and it also calls a link editor to link the C object files.

Your ESQL/C source file contains commands for the C preprocessor (directives of the form #directive). When you use the default order of compilation, these C directives have no effect on ESQL/C statements but take effect in the usual way when the C compiler processes the source file.

If you choose to run the C preprocessor on the ESQL/C source file before the ESQL/C preprocessor, you can use the C language #define and typedef directives to define ESQL/C host variables. For more information, see Running the C Preprocessor Before the ESQL/C Preprocessor.

The C compiler takes the following actions:

• Compiles the C language statements to object code
• Links to ESQL/C libraries as well as any other files or libraries you specify
• Creates an executable file

For information about command-line options that affect the compilation and linking steps, see Specifying a Particular C Compiler and Syntax of Additional Options for Windows.

Once you have created an ESQL/C program file, you run the esql command on that file. By default, the ESQL/C preprocessor runs first and translates the embedded SQL statements in the program into ESQL/C function calls that communicate with the database server. The ESQL/C preprocessor produces a C source file and calls the C compiler. The C compiler then preprocesses and compiles your source file and links any other C source file, object file, or library file the same way as any other C program. If esql does not encounter errors in one of these steps, it generates an executable file. You can run the compiled ESQL/C program as you would any C program. When the program runs, it calls the ESQL/C library procedures; the library procedures set up communications with the database server to carry out the SQL operations.

Figure 2-1 illustrates the process by which an ESQL/C program becomes an executable program.

Figure 2-1 Relationship Between INFORMIX-ESQL/C and C

Important: Keep in mind that with the default order of compilation, esql handles ESQL/C preprocessor directives before it calls the C compiler. Therefore, the ESQL/C directives take effect before the C compiler performs any preprocessing. You cannot access ESQL/C definitions within C preprocessor directives, nor can you use the C preprocessor to perform conditional compilation of ESQL/C statements.

Running the C Preprocessor First

ESQL/C allows you change the default order of processing when you compile your ESQL/C program. ESQL/C allows you to run the C preprocessor on the ESQL/C source file first, and then pass that file to the ESQL/C preprocessor. This feature enables your ESQL/C program to access variables made available by C preprocessor directives. For more information on this option, see Running the C Preprocessor Before the ESQL/C Preprocessor.