#include <stdio.h>
#include <errno.h>

#define BUFFER_SIZE 256

/* Simple program to read and append to a single PDS member via DD name. */
/* Author: Greg Gauthier */
/* Date: 2026-02-08 */
/* NOTE: No single-line comments due to MVS SYSIN/JCL interpretation. */

int main()
{
    FILE *fp_read;
    FILE *fp_append;
    char buffer[BUFFER_SIZE];

    /* First: open for reading only to dump current content */
    fp_read = fopen("dd:TESTDD", "r");
    if (fp_read == NULL)
    {
        perror("fopen read failed");
        printf("errno = %d\n", __errno());
        return 1;
    }

    printf("Existing content:\n");
    while (fgets(buffer, BUFFER_SIZE, fp_read) != NULL)
    {
        printf("%s", buffer);
    }
    fclose(fp_read);

    /* Second: open for append only to add the new line */
    fp_append = fopen("dd:TESTDD", "a");
    if (fp_append == NULL)
    {
        perror("fopen append failed");
        printf("errno = %d\n", __errno());
        return 1;
    }

    fprintf(fp_append, "Appended from C program!\n");
    fclose(fp_append);

    printf("Append complete.\n");

    return 0;
}