File Handling in COBOL: Sequential and Indexed Files

May 6, 2024

File handling is a crucial aspect of COBOL programming. This post discusses the concepts of sequential and indexed files, file organization, and how to perform file operations in COBOL programs.

Sequential Files

Sequential files in COBOL are accessed in a linear manner, from the beginning to the end of the file. These files are organized in a sequential order, and each record can be read only once in the order they are stored.

To work with sequential files in COBOL, you need to define the file structure using the FILE SECTION and FD (File Description) entries in the Data Division. Here is an example of defining a sequential file in COBOL:

SELECT file-name ASSIGN TO 'filename.dat'.
ORGANIZATION IS SEQUENTIAL.
FD file-name.
01 record-layout.
   ... (fields definition)

Once the file is defined, you can OPEN, READ, WRITE, and CLOSE the file using the appropriate file handling verbs in COBOL.

Indexed Files

Indexed files in COBOL use a key to access records directly. These files are organized based on the key values, allowing for random access to records. Indexed files are efficient for searching and retrieving specific records quickly.

To work with indexed files in COBOL, you need to define the file structure with an additional INDEXED BY clause in the FD entry. Here is an example of defining an indexed file in COBOL:

SELECT file-name ASSIGN TO 'filename.idx'.
ORGANIZATION IS INDEXED.
ACCESS MODE IS DYNAMIC.
RECORD KEY IS key-field.
FD file-name.
01 record-layout.
   ... (fields definition)

Similar to sequential files, you can OPEN, READ, WRITE, and CLOSE indexed files using the appropriate file handling verbs in COBOL.

Understanding file handling in COBOL is essential for developing applications that interact with external data sources. By mastering sequential and indexed files, you can efficiently manage data within your COBOL programs.