break read and append into two operations

jcl/TXTWKR01.jcl

@@ -1,5 +1,5 @@
 //TXTWKR01   JOB (GCC),'File I/O Example',
-//             NOTIFY=@05054,CLASS=A,MSGCLASS=A,
+//             NOTIFY=@05054,CLASS=A,MSGCLASS=H,
 //             MSGLEVEL=(1,1),REGION=4M,TIME=1440
 //* Compile and Go Step
 //STEP1 EXEC GCCCG,INFILE='@05054.SRCLIB.C(TXTWKR01)'

src/TXTWKR01.c

@@ -10,35 +10,39 @@
 
 int main()
 {
-    FILE *fp;
+    FILE *fp_read;
+    FILE *fp_append;
     char buffer[BUFFER_SIZE];
 
-    /* Open the file in update mode (read and write). */
+    /* First: open for reading only to dump current content */
-    /* The filename is "dd:DDNAME" where DDNAME is defined in JCL. */
+    fp_read = fopen("dd:TESTDD", "r");
-    fp = fopen("dd:TESTDD", "a+");
+    if (fp_read == NULL)
-    if (fp == NULL)
     {
-        perror("fopen failed.");
+        perror("fopen read failed");
         printf("errno = %d\n", __errno());
         return 1;
     }
 
-    /* Read and print existing lines (to SYSOUT). */
     printf("Existing content:\n");
-    while (fgets(buffer, BUFFER_SIZE, fp) != NULL)
+    while (fgets(buffer, BUFFER_SIZE, fp_read) != NULL)
     {
         printf("%s", buffer);
     }
+    fclose(fp_read);
 
-    /* After reading to EOF, the file position is at the end, so we can append. */
+    /* Second: open for append only to add the new line */
-    fprintf(fp, "Appended from C program!\n");
+    fp_append = fopen("dd:TESTDD", "a");
+    if (fp_append == NULL)
+    {
+        perror("fopen append failed");
+        printf("errno = %d\n", __errno());
+        return 1;
+    }
 
-    /* Close the file. */
+    fprintf(fp_append, "Appended from C program!\n");
-    fclose(fp);
+    fclose(fp_append);
 
     printf("Append complete.\n");
 
     return 0;
 }
-
-