The UTL_FILE.FOPEN_NCHAR function in Oracle PL/SQL is used to open a file for reading or writing in Unicode (NCHAR) mode. This function is part of the UTL_FILE package, which allows PL/SQL programs to read from and write to files stored in the operating system’s file system. The FOPEN_NCHAR function is specifically designed to handle multibyte character sets, ensuring that Unicode data is correctly read from or written to the file.
Key Differences from FOPEN
The primary difference between UTL_FILE.FOPEN_NCHAR and the standard UTL_FILE.FOPEN is that FOPEN_NCHAR is intended for working with files that contain Unicode data. This makes it useful for applications that need to support internationalization, where files contain characters from various languages.
Syntax
UTL_FILE.FOPEN_NCHAR ( location IN VARCHAR2, filename IN VARCHAR2, open_mode IN VARCHAR2, max_linesize IN BINARY_INTEGER DEFAULT NULL ) RETURN UTL_FILE.FILE_TYPE;
location: A directory object or the name of a directory accessible by the database where the file resides.
filename: The name of the file you want to open.
open_mode: The mode in which the file is opened. Common modes are:
‘r’ for reading
‘w’ for writing (will overwrite the file if it exists)
‘a’ for appending to the file
max_linesize: The maximum number of characters for each line read from or written to the file. The default value is 1024 characters, but it can be set to a higher value as required.
Example
DECLARE
file_handle UTL_FILE.FILE_TYPE;
line_content NVARCHAR2(100);
BEGIN
-- Open a Unicode file for reading
file_handle := UTL_FILE.FOPEN_NCHAR('MY_DIR', 'test_unicode.txt', 'r');
-- Read a line from the file
UTL_FILE.GET_LINE_NCHAR(file_handle, line_content);
-- Process the line content here (e.g., print to console, log, etc.)
DBMS_OUTPUT.PUT_LINE('Line content: ' || line_content);
-- Close the file after processing
UTL_FILE.FCLOSE(file_handle);
END;
/
Key Points
Multibyte Characters: This function ensures that multibyte (Unicode) characters are correctly handled when reading or writing files.
File Modes: The same modes (‘r’, ‘w’, ‘a’) apply as in the non-NCHAR version, but with the addition of Unicode support.
Max Line Size: You can control the maximum line size, which can be useful when dealing with large lines of text.
Error Handling
When working with UTL_FILE.FOPEN_NCHAR, the following errors can occur:
INVALID_PATH: The specified directory object is invalid or does not exist.
INVALID_MODE: The open_mode argument is not valid.
INVALID_OPERATION: The file is being accessed in an unsupported manner (e.g., trying to write to a read-only file).
READ_ERROR or WRITE_ERROR: Errors in reading from or writing to the file.
Conclusion
The UTL_FILE.FOPEN_NCHAR function is essential when dealing with file operations involving Unicode data. It ensures that multibyte character sets are handled correctly, making it a good choice for globalized applications.