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g 'Value' to Your Prototypes | IBM i | IBM Systems Magazine http://www.ibmsystemsmag.com/ibmi/december04/spotlight/8303p3.aspx

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STORAGEPRODUCT NEWSENDPGMBUYER'S GUIDE

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Adding 'Value' to Your PrototypesDecember 2004 | by Jon Paris and Susan Gantner

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Note that the prototype specifies CmdString as being a pointer, passed by VALUE. By using Options(*String), we have allowed ourselves to pass the variableCommand, and the compiler does the w ork for us. The result is that we can pass a character field (not a pointer) to the function on the call. If you use a regular RPGvariable, rather than the variable-length field, remember to use %Trim when passing the parameter. If you're running V5R3 or later, you can avoid this by codingOptions(*Trim) on the parameter.

We've covered the basic prototyping information to make use o f the C-function library, including the use of EXTPROC, VALUE and OPTIONS(*STRING). Somemore advanced C functions require the use of call-back procedures in your RPG program. Click here for an example of using this with the qsort function.

In the meantime, a few more details are necessary to make all of this work. First, you must specify the Binding Directory name QC2LE, preferably on your RPGprograms H spec. This is the binding directory that references all of the service programs in the C-function library. The system binder needs this to locate thefunctions w hen creating your program.

If you prefer to use the Create Bound RPG (CRTBNDRPG) command (or option 14 in PDM) to compile your code, you must also specify DFTACTGRP(*NO) toallow for bound calls. This can also be specified on the H spec. Here's how your H spec might appear:

H BndDir('QC2LE') DftActGrp(*No)

More Information

If you find a C function that you would like to use and need some help in translating the C data types into RPG data types, you can find that information as well assome other examples on calling C functions from RPG in the IBM Redbook, "Who Knew You Could Do That with RPG IV?"

Try your hand at using C functions to open up your code to the C-function librarys power.

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Jon Paris is a technical editor with IBM Systems Magazine and co-owner of Partner400.

More Articles From Jon Paris

Susan Gantner is a technical editor with IBM Systems Magazine and co-owner of Partner400.

More Articles From Susan Gantner

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