File Operations in RPG
In RPG, handling data files is essential for managing input and output operations. This topic will cover the fundamental operations that you can perform on files: opening, reading, writing, and closing.
1. Opening a File
To work with a file in RPG, the first step is to open it. You can open a file using the OPEN operation code. The syntax is:
`rpg
OPEN file-name
`
Example of Opening a File
`rpg
Dcl-F myFile DISK; // Declare the file
// Opening the file for input
OPEN myFile;
`
2. Reading from a File
Once the file is opened, you can read data from it using the READ operation code. This operation reads a single record from the file into a record format.
Example of Reading from a File
`rpg
Dcl-F myFile DISK; // Declare the file
Dcl-DS recordFormat;
field1 Char(20);
field2 Int(10);
End-Ds;
// Read the first record from the file READ myFile recordFormat;
// Check if the read was successful
If %EOF(myFile);
// Handle end of file
EndIf;
`
3. Writing to a File
To write data to a file, you use the WRITE operation code. This writes the contents of a record format into the file.
Example of Writing to a File
`rpg
Dcl-F myFile DISK; // Declare the file
Dcl-DS recordFormat;
field1 Char(20);
field2 Int(10);
End-Ds;
// Assign values to the fields recordFormat.field1 = 'Data Entry'; recordFormat.field2 = 123;
// Write the record to the file
WRITE myFile recordFormat;
`
4. Closing a File
After completing the file operations, it is important to close the file using the CLOSE operation code. This ensures that all resources are released properly.
Example of Closing a File
`rpg
CLOSE myFile;
`
Practical Example
Let’s combine all these operations into a simple RPG program that reads from an input file, processes the data, and writes the results to an output file.
`rpg
Dcl-F inputFile DISK; // Input file declaration
Dcl-F outputFile DISK; // Output file declaration
Dcl-DS recordFormat;
field1 Char(20);
field2 Int(10);
End-Ds;
// Open files OPEN inputFile; OPEN outputFile;
// Read records from input file, process, and write to output file READ inputFile recordFormat; While not %EOF(inputFile); // Process data (e.g., just writing it back for this example) WRITE outputFile recordFormat; READ inputFile recordFormat; EndWhile;
// Close files
CLOSE inputFile;
CLOSE outputFile;
`
Summary
In summary, file operations in RPG are crucial for data manipulation. By properly opening, reading, writing, and closing files, you can effectively manage data input and output within your RPG applications.