From 7fac298167389228750877573437df8c81884d7c Mon Sep 17 00:00:00 2001
From: Quincey Koziol <koziol@hdfgroup.org>
Date: Tue, 23 Mar 1999 16:48:57 -0500
Subject: [svn-r1161] Modified H5Aread to fill the user's buffer with zero's
 (the fill value for uninitialized attributes) if they read the attribute
 before any data is written to it or it's stored on disk.

---
 src/H5A.c | 66 ++++++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 36 insertions(+), 30 deletions(-)

diff --git a/src/H5A.c b/src/H5A.c
index d5168d6..9ef6df5 100644
--- a/src/H5A.c
+++ b/src/H5A.c
@@ -754,7 +754,7 @@ H5Aread(hid_t attr_id, hid_t type_id, void *buf)
  ERRORS
 
  DESCRIPTION
-    This function read a complete attribute to disk.
+    This function reads a complete attribute from disk.
 --------------------------------------------------------------------------*/
 static herr_t
 H5A_read(H5A_t *attr, const H5T_t *mem_type, void *buf)
@@ -781,39 +781,45 @@ H5A_read(H5A_t *attr, const H5T_t *mem_type, void *buf)
     src_type_size = H5T_get_size(attr->dt);
     dst_type_size = H5T_get_size(mem_type);
 
-    /* Get the maximum buffer size needed and allocate it */
-    buf_size = nelmts*MAX(src_type_size,dst_type_size);
-    if (NULL==(tconv_buf = H5MM_malloc (buf_size))) {
-	HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
-		     "memory allocation failed");
-    }
-
-    /* Copy the attribute data into the buffer for conversion */
-    HDmemcpy(tconv_buf,attr->data,src_type_size*nelmts);
+    /* Check if the attribute has any data yet, if not, fill with zeroes */
+    if(attr->ent_opened && !attr->initialized) {
+        HDmemset(buf,0,dst_type_size*nelmts);
+    }   /* end if */
+    else {  /* Attribute exists and has a value */
+        /* Get the maximum buffer size needed and allocate it */
+        buf_size = nelmts*MAX(src_type_size,dst_type_size);
+        if (NULL==(tconv_buf = H5MM_malloc (buf_size))) {
+        HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                 "memory allocation failed");
+        }
 
-    /* Convert memory buffer into disk buffer */
-    /* Set up type conversion function */
-    if (NULL == (tpath = H5T_path_find(attr->dt, mem_type, NULL, NULL))) {
-        HGOTO_ERROR(H5E_ATTR, H5E_UNSUPPORTED, FAIL,
-		    "unable to convert between src and dest data types");
-    } else if (!H5T_IS_NOOP(tpath)) {
-        if ((src_id = H5I_register(H5I_DATATYPE,
-				   H5T_copy(attr->dt, H5T_COPY_ALL)))<0 ||
-	    (dst_id = H5I_register(H5I_DATATYPE,
-				   H5T_copy(mem_type, H5T_COPY_ALL)))<0) {
-            HGOTO_ERROR(H5E_ATTR, H5E_CANTREGISTER, FAIL,
-			"unable to register types for conversion");
+        /* Copy the attribute data into the buffer for conversion */
+        HDmemcpy(tconv_buf,attr->data,src_type_size*nelmts);
+
+        /* Convert memory buffer into disk buffer */
+        /* Set up type conversion function */
+        if (NULL == (tpath = H5T_path_find(attr->dt, mem_type, NULL, NULL))) {
+            HGOTO_ERROR(H5E_ATTR, H5E_UNSUPPORTED, FAIL,
+                "unable to convert between src and dest data types");
+        } else if (!H5T_IS_NOOP(tpath)) {
+            if ((src_id = H5I_register(H5I_DATATYPE,
+                       H5T_copy(attr->dt, H5T_COPY_ALL)))<0 ||
+            (dst_id = H5I_register(H5I_DATATYPE,
+                       H5T_copy(mem_type, H5T_COPY_ALL)))<0) {
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTREGISTER, FAIL,
+                "unable to register types for conversion");
+            }
         }
-    }
 
-    /* Perform data type conversion.  */
-    if (H5T_convert(tpath, src_id, dst_id, nelmts, tconv_buf, NULL)<0) {
-	HGOTO_ERROR(H5E_ATTR, H5E_CANTENCODE, FAIL,
-		    "data type conversion failed");
-    }
+        /* Perform data type conversion.  */
+        if (H5T_convert(tpath, src_id, dst_id, nelmts, tconv_buf, NULL)<0) {
+        HGOTO_ERROR(H5E_ATTR, H5E_CANTENCODE, FAIL,
+                "data type conversion failed");
+        }
 
-    /* Copy the converted data into the user's buffer */
-    HDmemcpy(buf,tconv_buf,dst_type_size*nelmts);
+        /* Copy the converted data into the user's buffer */
+        HDmemcpy(buf,tconv_buf,dst_type_size*nelmts);
+    } /* end else */
 
     ret_value=SUCCEED;
 
-- 
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