Calling a Compiled C Program from Another C Program in ILE C on AS/400

Learn how to effectively call a compiled C program from another C program in `ILE C` on AS/400 while passing arguments by reference. Discover alternative solutions for better integration.
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Calling a Compiled C Program from Another C Program in ILE C on AS/400

In the world of programming, especially when it comes to AS/400 systems, developers often face unique challenges. One such challenge is the need to call a compiled C program from another C program while passing arguments by reference. This is a common requirement, especially for those transitioning from other programming languages like COBOL. In this guide, we will explore how to accomplish this in ILE C on AS/400, along with a detailed solution breakdown.

Understanding the Problem

The initial setup involves trying to use the execlp function, which works seamlessly on Linux but is not recognized in the AS/400 environment. As a result, developers need to find another method to call one C program from another while managing to pass arguments effectively.

Why execlp Doesn't Work

execlp is a Unix-based function, part of the POSIX standard.

It is not supported in the AS/400 ILE C environment, which requires different methods for inter-program communication.

The Solution: Using -pragma and QCMDEXC

To overcome these limitations, we can utilize the -pragma compiler directive along with the QCMDEXC (Command Execute) API to achieve the desired functionality. This method allows you to pass the arguments by reference in a more controlled environment.

Step-by-Step Breakdown

Include Necessary Headers: Begin by including the required headers for your program.

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Define Program Binding: Use the -pragma directive to define the program name and set the linkage type. This is essential for calling AS/400 commands effectively.

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Initialize Arguments: In this step, you will declare your arguments and initialize them for the command execution.

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Construct Your Command: Here, build the command string that you'd like to execute. For instance, you can model a job delay command.

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Call the Command: Finally, use the qcmdexc function to execute the command with the arguments passed by reference.

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Why This Works

All ILE programs, regardless of whether they are written in C or COBOL, follow a unified interface, allowing you to execute them using the proper APIs. This consistency across the platform provides the flexibility we need for inter-program interactions.

Conclusion

Though calling one compiled C program from another in ILE C on AS/400 may initially seem daunting, utilizing the -pragma directive along with the QCMDEXC API is an effective solution. This approach ensures that arguments can be passed by reference, similar to how you would do in COBOL. With this knowledge, you can enhance your programs' functionality and achieve better integration across your applications.

By understanding these key strategies, AS/400 developers can confidently tackle inter-program communications, facilitating smoother operations and broader program capabilities.