COBOL COL Function

The COL function in COBOL is used for column positioning in screen handling and report formatting. It provides precise control over cursor positioning, data alignment, and screen layout management in interactive and batch applications.

Overview and Purpose

The COL function serves as a fundamental tool for controlling horizontal positioning in COBOL screen and report applications. Whether you're developing interactive terminal applications, generating formatted reports, or creating user interfaces, the COL function provides the precision needed to align data, position cursors, and create professional-looking output.

In modern mainframe environments, proper screen formatting is crucial for user experience and data presentation. The COL function works in conjunction with other positioning functions to create well-structured displays that are both functional and visually appealing.

Basic Syntax and Usage

1
DISPLAY "Customer Name:" AT COL 10

This basic example demonstrates how to position text at a specific column on the screen. The COL 10 specification places the text "Customer Name:" starting at column 10 of the current line. This type of precise positioning is essential for creating aligned forms and structured data displays where consistency and readability are important.

Screen Field Positioning

1
2
DISPLAY "ID:" AT COL 5
DISPLAY CUSTOMER-ID AT COL 10

This example shows how to create aligned field labels and data. The label "ID:" is positioned at column 5, while the actual customer ID data is displayed at column 10. This creates a consistent alignment pattern that makes forms easier to read and data easier to locate. The spacing between the label and data provides visual separation while maintaining the logical relationship between them.

Dynamic Column Calculation

1
2
COMPUTE WS-COL-POSITION = 10 + (WS-FIELD-NUMBER * 15)
DISPLAY WS-DATA-FIELD AT COL WS-COL-POSITION

This technique demonstrates dynamic column positioning based on calculated values. The column position is computed using a base position (10) plus an offset calculated from the field number multiplied by the field width (15). This approach is particularly useful when creating tabular displays or when the number of columns varies based on runtime conditions or user configuration.

Report Header Formatting

1
2
3
DISPLAY "CUSTOMER REPORT" AT COL 30
DISPLAY "Page: " AT COL 60
DISPLAY WS-PAGE-NUMBER AT COL 66

This example illustrates how to create a formatted report header with multiple elements positioned at specific columns. The main title "CUSTOMER REPORT" is centered at column 30, while the page information is right-aligned starting at column 60. This type of header formatting creates professional-looking reports with clear visual hierarchy and easy navigation for users reviewing printed or displayed output.

Form Layout Creation

1
2
3
DISPLAY "Name:" AT COL 5
DISPLAY "Address:" AT COL 5  
DISPLAY "Phone:" AT COL 5

This form layout example shows how to align field labels vertically by using the same column position for each label. All labels start at column 5, creating a clean, aligned appearance that guides the user's eye down the form. This consistent alignment is a fundamental principle of good user interface design and helps reduce data entry errors by making the form structure clear and predictable.

Data Validation Display

1
2
3
4
IF INPUT-ERROR
    DISPLAY "ERROR: Invalid input" AT COL 20
    DISPLAY "Please re-enter" AT COL 25
END-IF

This validation example demonstrates how to position error messages at specific columns to draw attention and provide clear feedback to users. The error message is positioned at column 20, while the instruction is slightly indented at column 25. This visual hierarchy helps users quickly identify the problem and understand what action they need to take to correct it.

Table Column Headers

1
2
3
DISPLAY "ID" AT COL 1
DISPLAY "Name" AT COL 10
DISPLAY "Amount" AT COL 35

This table header example shows how to position column headers for tabular data display. Each header is positioned at the appropriate column to align with the data that will appear below it. The ID column starts at position 1, the Name column at position 10, and the Amount column at position 35. This creates clear column boundaries and makes it easy for users to associate data with the correct column headers.

Interactive Menu Positioning

1
2
3
4
DISPLAY "MAIN MENU" AT COL 35
DISPLAY "1. Customer Entry" AT COL 25
DISPLAY "2. Reports" AT COL 25
DISPLAY "Selection:" AT COL 25

This menu example demonstrates how to create a centered menu title with consistently aligned menu options. The title "MAIN MENU" is positioned at column 35 for centering, while all menu options and the selection prompt are aligned at column 25. This creates a visually balanced menu that is easy to read and navigate, with clear visual hierarchy between the title and the options.

Conditional Column Positioning

1
2
3
4
5
6
IF WS-DISPLAY-MODE = 'COMPACT'
    MOVE 5 TO WS-COL-START
ELSE
    MOVE 15 TO WS-COL-START
END-IF
DISPLAY WS-DATA AT COL WS-COL-START

This example shows how to implement conditional column positioning based on display modes or user preferences. In compact mode, data starts at column 5 to maximize screen usage, while in normal mode, data starts at column 15 for better readability. This flexibility allows applications to adapt to different screen sizes, user preferences, or operational requirements while maintaining consistent functionality.

Multi-Line Form Alignment

1
2
3
4
DISPLAY "Customer Information" AT COL 20
DISPLAY "First Name:" AT COL 5
DISPLAY "Last Name:" AT COL 5
DISPLAY "Email:" AT COL 5

This multi-line form demonstrates how to create a structured data entry screen with a centered title and consistently aligned field labels. The title is positioned at column 20 for visual centering, while all field labels are aligned at column 5. This creates a clean, professional appearance that helps users understand the form structure and reduces the likelihood of data entry errors.

Status Message Positioning

1
2
3
DISPLAY "Processing..." AT COL 30
PERFORM LONG-RUNNING-PROCESS
DISPLAY "Complete!" AT COL 35

This status message example shows how to position feedback messages to provide users with clear information about system status. The "Processing..." message is centered at column 30, while the completion message is positioned slightly to the right at column 35. This positioning helps draw attention to status changes and keeps users informed about system operations, which is particularly important for long-running processes.

Performance Considerations

1
2
3
01  WS-SCREEN-BUFFER.
    05  WS-LINE-DATA        PIC X(80).
    05  WS-CURSOR-POSITION  PIC 99.

When using COL positioning extensively, consider implementing screen buffering to improve performance. This structure allows you to build complete screen lines in memory before displaying them, reducing the number of individual DISPLAY operations. Screen buffering is particularly beneficial when creating complex layouts or when performance is critical, such as in high-volume transaction processing applications.

Error Handling and Validation

1
2
3
4
IF WS-COL-POSITION < 1 OR WS-COL-POSITION > 80
    DISPLAY "Invalid column position"
    MOVE 1 TO WS-COL-POSITION
END-IF

This validation routine ensures that column positions are within valid screen boundaries. Most terminal screens support 80 columns, so this check prevents positioning errors that could cause display problems or runtime errors. When an invalid position is detected, the routine displays an error message and resets the position to a safe default value. This type of defensive programming is essential for robust screen handling applications.

Best Practices for Column Positioning

Consistent Alignment

Maintain consistent column positions throughout your application to create a professional appearance and improve user experience. Define standard column positions for common elements like field labels, data fields, and buttons, and use these consistently across all screens.

Screen Width Considerations

Always consider the target screen width when designing column layouts. Traditional mainframe terminals typically support 80 columns, but modern environments may support wider displays. Design your layouts to work well within the constraints of your target environment.

Accessibility and Readability

Ensure that your column positioning creates readable layouts with adequate spacing between elements. Avoid cramped layouts that make data difficult to read or distinguish. Consider users with visual impairments who may need larger fonts or higher contrast displays.

Integration with Modern Interfaces

1
2
3
4
DISPLAY "Web Service Status:" AT COL 5
DISPLAY WS-SERVICE-STATUS AT COL 25
DISPLAY "Response Time:" AT COL 45
DISPLAY WS-RESPONSE-TIME AT COL 60

This example shows how COL positioning can be used to display information from modern system integrations, such as web service calls or API responses. The structured layout makes it easy for operators to monitor system status and performance metrics. This type of display is particularly valuable in hybrid environments where COBOL applications interface with modern web services and cloud platforms.