COBOL Tutorial

COBOL CDECL Clause

The CDECL clause in COBOL specifies the use of C calling conventions when interfacing with C language functions and libraries. This clause is essential for cross-language programming, enabling COBOL programs to call C functions with proper parameter passing, stack management, and return value handling. CDECL ensures compatibility between COBOL and C code, making it possible to leverage existing C libraries, system APIs, and modern programming frameworks within COBOL applications while maintaining proper calling convention standards.

Understanding CDECL Clause

CDECL (C Declaration) specifies that a COBOL program should use C language calling conventions when calling external functions. This includes parameter passing order, stack cleanup responsibility, and return value conventions that match C standards.

Key Features:

C-compatible parameter passing
Proper stack management
Standard return value handling
Cross-language interoperability
Library integration support

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*> Basic CDECL usage for C function calls
DATA DIVISION.
WORKING-STORAGE SECTION.
01  C-LIBRARY-INTERFACE.
    05  STRING-LENGTH     PIC 9(8) COMP.
    05  RESULT-CODE       PIC S9(8) COMP.
    05  ERROR-MESSAGE     PIC X(256).
 
01  C-FUNCTION-PARAMETERS.
    05  INPUT-STRING      PIC X(100).
    05  OUTPUT-BUFFER     PIC X(200).
    05  BUFFER-SIZE       PIC 9(8) COMP VALUE 200.
 
PROCEDURE DIVISION.
CALL-C-FUNCTIONS.
    *> Call C strlen function
    MOVE "Hello, World!" TO INPUT-STRING
    CALL "strlen" USING BY REFERENCE INPUT-STRING
        RETURNING STRING-LENGTH
        ON EXCEPTION
            DISPLAY "Error calling strlen function"
        NOT ON EXCEPTION
            DISPLAY "String length: " STRING-LENGTH
    END-CALL.
 
    *> Call C sprintf function with CDECL convention
    CALL "sprintf" USING 
        BY REFERENCE OUTPUT-BUFFER
        BY REFERENCE "Number: %d, String: %s"
        BY VALUE 42
        BY REFERENCE "Test"
        RETURNING RESULT-CODE
        ON EXCEPTION
            DISPLAY "Error calling sprintf function"
    END-CALL.

Advanced C Library Integration

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*> Advanced C library integration with CDECL
DATA DIVISION.
WORKING-STORAGE SECTION.
01  MATH-LIBRARY-INTERFACE.
    05  DOUBLE-PRECISION-A    COMP-2 VALUE 3.14159.
    05  DOUBLE-PRECISION-B    COMP-2 VALUE 2.71828.
    05  MATH-RESULT           COMP-2.
    05  INT-PARAMETER         PIC S9(8) COMP VALUE 12345.
 
01  FILE-SYSTEM-INTERFACE.
    05  FILE-HANDLE           POINTER.
    05  FILE-NAME             PIC X(256) VALUE "data.txt".
    05  FILE-MODE             PIC X(10) VALUE "r".
    05  BYTES-READ            PIC 9(8) COMP.
    05  READ-BUFFER           PIC X(1024).
 
01  MEMORY-MANAGEMENT.
    05  MEMORY-POINTER        POINTER.
    05  MEMORY-SIZE           PIC 9(8) COMP VALUE 1024.
    05  ALLOCATION-RESULT     PIC S9(8) COMP.
 
PROCEDURE DIVISION.
ADVANCED-C-INTEGRATION.
    PERFORM MATH-LIBRARY-CALLS
    PERFORM FILE-SYSTEM-OPERATIONS
    PERFORM MEMORY-MANAGEMENT-CALLS.
 
MATH-LIBRARY-CALLS.
    *> Call C math library functions
    CALL "sqrt" USING BY VALUE DOUBLE-PRECISION-A
        RETURNING MATH-RESULT
        ON EXCEPTION
            DISPLAY "Error calling sqrt function"
        NOT ON EXCEPTION
            DISPLAY "Square root result: " MATH-RESULT
    END-CALL
    
    CALL "pow" USING 
        BY VALUE DOUBLE-PRECISION-A
        BY VALUE DOUBLE-PRECISION-B
        RETURNING MATH-RESULT
        ON EXCEPTION
            DISPLAY "Error calling pow function"
        NOT ON EXCEPTION
            DISPLAY "Power result: " MATH-RESULT
    END-CALL
    
    CALL "sin" USING BY VALUE DOUBLE-PRECISION-A
        RETURNING MATH-RESULT
        ON EXCEPTION
            DISPLAY "Error calling sin function"
        NOT ON EXCEPTION
            DISPLAY "Sine result: " MATH-RESULT
    END-CALL.
 
FILE-SYSTEM-OPERATIONS.
    *> C file operations
    CALL "fopen" USING 
        BY REFERENCE FILE-NAME
        BY REFERENCE FILE-MODE
        RETURNING FILE-HANDLE
        ON EXCEPTION
            DISPLAY "Error opening file"
        NOT ON EXCEPTION
            IF FILE-HANDLE NOT = NULL
                PERFORM READ-FILE-CONTENTS
                PERFORM CLOSE-FILE
            ELSE
                DISPLAY "Failed to open file"
            END-IF
    END-CALL.
 
READ-FILE-CONTENTS.
    CALL "fread" USING 
        BY REFERENCE READ-BUFFER
        BY VALUE 1
        BY VALUE 1024
        BY VALUE FILE-HANDLE
        RETURNING BYTES-READ
        ON EXCEPTION
            DISPLAY "Error reading file"
        NOT ON EXCEPTION
            DISPLAY "Read " BYTES-READ " bytes from file"
    END-CALL.
 
CLOSE-FILE.
    CALL "fclose" USING BY VALUE FILE-HANDLE
        RETURNING RESULT-CODE
        ON EXCEPTION
            DISPLAY "Error closing file"
    END-CALL.
 
MEMORY-MANAGEMENT-CALLS.
    *> Dynamic memory allocation
    CALL "malloc" USING BY VALUE MEMORY-SIZE
        RETURNING MEMORY-POINTER
        ON EXCEPTION
            DISPLAY "Error allocating memory"
        NOT ON EXCEPTION
            IF MEMORY-POINTER NOT = NULL
                DISPLAY "Memory allocated successfully"
                PERFORM USE-ALLOCATED-MEMORY
                PERFORM FREE-MEMORY
            ELSE
                DISPLAY "Memory allocation failed"
            END-IF
    END-CALL.
 
FREE-MEMORY.
    CALL "free" USING BY VALUE MEMORY-POINTER
        ON EXCEPTION
            DISPLAY "Error freeing memory"
        NOT ON EXCEPTION
            DISPLAY "Memory freed successfully"
    END-CALL.

System API Integration

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*> System API integration using CDECL conventions
DATA DIVISION.
WORKING-STORAGE SECTION.
01  SYSTEM-API-INTERFACE.
    05  PROCESS-ID            PIC 9(8) COMP.
    05  COMMAND-LINE          PIC X(512).
    05  SYSTEM-RESULT         PIC S9(8) COMP.
    05  ENVIRONMENT-VAR       PIC X(256).
    05  VAR-VALUE             PIC X(512).
 
01  TIME-FUNCTIONS.
    05  TIME-VALUE            PIC 9(10) COMP.
    05  TIME-STRUCT           PIC X(36).
    05  FORMATTED-TIME        PIC X(100).
 
01  NETWORK-OPERATIONS.
    05  SOCKET-DESCRIPTOR     PIC S9(8) COMP.
    05  IP-ADDRESS            PIC X(16) VALUE "127.0.0.1".
    05  PORT-NUMBER           PIC 9(5) COMP VALUE 8080.
    05  NETWORK-BUFFER        PIC X(2048).
 
PROCEDURE DIVISION.
SYSTEM-API-CALLS.
    PERFORM TIME-SYSTEM-CALLS
    PERFORM PROCESS-MANAGEMENT
    PERFORM ENVIRONMENT-ACCESS
    PERFORM NETWORK-FUNCTIONS.
 
TIME-SYSTEM-CALLS.
    *> Get current time
    CALL "time" USING BY REFERENCE TIME-VALUE
        RETURNING TIME-VALUE
        ON EXCEPTION
            DISPLAY "Error getting system time"
        NOT ON EXCEPTION
            DISPLAY "Current time: " TIME-VALUE
    END-CALL
    
    *> Convert time to structure
    CALL "localtime" USING BY REFERENCE TIME-VALUE
        RETURNING TIME-STRUCT
        ON EXCEPTION
            DISPLAY "Error converting time"
    END-CALL
    
    *> Format time string
    CALL "strftime" USING 
        BY REFERENCE FORMATTED-TIME
        BY VALUE 100
        BY REFERENCE "%Y-%m-%d %H:%M:%S"
        BY REFERENCE TIME-STRUCT
        RETURNING STRING-LENGTH
        ON EXCEPTION
            DISPLAY "Error formatting time"
        NOT ON EXCEPTION
            DISPLAY "Formatted time: " FORMATTED-TIME
    END-CALL.
 
PROCESS-MANAGEMENT.
    *> Get process ID
    CALL "getpid" RETURNING PROCESS-ID
        ON EXCEPTION
            DISPLAY "Error getting process ID"
        NOT ON EXCEPTION
            DISPLAY "Process ID: " PROCESS-ID
    END-CALL
    
    *> Execute system command
    MOVE "ls -la" TO COMMAND-LINE
    CALL "system" USING BY REFERENCE COMMAND-LINE
        RETURNING SYSTEM-RESULT
        ON EXCEPTION
            DISPLAY "Error executing system command"
        NOT ON EXCEPTION
            DISPLAY "Command result: " SYSTEM-RESULT
    END-CALL.
 
ENVIRONMENT-ACCESS.
    *> Get environment variable
    MOVE "PATH" TO ENVIRONMENT-VAR
    CALL "getenv" USING BY REFERENCE ENVIRONMENT-VAR
        RETURNING VAR-VALUE
        ON EXCEPTION
            DISPLAY "Error getting environment variable"
        NOT ON EXCEPTION
            DISPLAY "PATH: " VAR-VALUE
    END-CALL.
 
NETWORK-FUNCTIONS.
    *> Create socket (basic example)
    CALL "socket" USING 
        BY VALUE 2      *> AF_INET
        BY VALUE 1      *> SOCK_STREAM
        BY VALUE 0      *> Protocol
        RETURNING SOCKET-DESCRIPTOR
        ON EXCEPTION
            DISPLAY "Error creating socket"
        NOT ON EXCEPTION
            IF SOCKET-DESCRIPTOR >= 0
                DISPLAY "Socket created: " SOCKET-DESCRIPTOR
                PERFORM CLOSE-SOCKET
            ELSE
                DISPLAY "Socket creation failed"
            END-IF
    END-CALL.
 
CLOSE-SOCKET.
    CALL "close" USING BY VALUE SOCKET-DESCRIPTOR
        RETURNING SYSTEM-RESULT
        ON EXCEPTION
            DISPLAY "Error closing socket"
    END-CALL.

Best Practices

CDECL Guidelines:

Use BY VALUE for simple data types passed to C functions
Use BY REFERENCE for strings and complex structures
Handle null pointers appropriately
Include proper error handling for C function calls
Understand C calling convention parameter order
Validate return codes and error conditions
Match COBOL data types to C equivalents correctly

COBOL Tutorial

COBOL CDECL Clause

Understanding CDECL Clause

Key Features:

Advanced C Library Integration

System API Integration

Best Practices

CDECL Guidelines:

Related Topics