diff --git a/examples/C/Makefile.am b/examples/C/Makefile.am
index 42c1d213c..7221eb247 100644
--- a/examples/C/Makefile.am
+++ b/examples/C/Makefile.am
@@ -18,6 +18,7 @@ check_PROGRAMS = collective_write \
                  column_wise \
                  block_cyclic \
                  flexible_api \
+                 flexible_bottom \
                  get_info \
                  hints \
                  mput \
@@ -30,6 +31,7 @@ check_PROGRAMS = collective_write \
                  transpose \
                  transpose2D \
                  vard_int \
+                 vard_bottom \
                  i_varn_int64 \
                  bput_varn_uint \
                  bput_varn_int64 \
diff --git a/examples/C/flexible_bottom.c b/examples/C/flexible_bottom.c
new file mode 100644
index 000000000..a41208abe
--- /dev/null
+++ b/examples/C/flexible_bottom.c
@@ -0,0 +1,215 @@
+/*********************************************************************
+ *
+ *  Copyright (C) 2024, Northwestern University and Argonne National Laboratory
+ *  See COPYRIGHT notice in top-level directory.
+ *
+ *********************************************************************/
+
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ *
+ * This example shows how to use PnetCDF blocking and nonblocking flexible APIs
+ * by supplying an MPI derived datatype and MPI_BOTTOM in the buffer argument.
+ * The MPI derived datatype is constructed through MPI_Type_create_hindexed(),
+ * which defines a noncontiguous memory space consisting of two separate blocks.
+ *
+ * A 2D global variable of size NY * NX * nprocs of type float is defined in
+ * the file. Each process allocates two write buffers and constructs an MPI
+ * derived datatype for the two buffers.
+ *
+ * The compile and run commands are given below.
+ *
+ *    % mpicc -O2 -o flexible_bottom flexible_bottom.c -lpnetcdf
+ *
+ *    % mpiexec -l -n 4 ./flexible_bottom ./testfile.nc
+ *
+ *    % ncmpidump ./testfile.nc
+ *    netcdf testfile {
+ *    // file format: CDF-5 (big variables)
+ *    dimensions:
+ *            Y = 4 ;
+ *            X = 16 ;
+ *    variables:
+ *            float var(Y, X) ;
+ *    data:
+ *
+ *     var =
+ *      10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13,
+ *      10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13,
+ *      50, 50, 50, 50, 51, 51, 51, 51, 52, 52, 52, 52, 53, 53, 53, 53,
+ *      50, 50, 50, 50, 51, 51, 51, 51, 52, 52, 52, 52, 53, 53, 53, 53 ;
+ *    }
+ *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h> /* strcpy(), strncpy() */
+#include <unistd.h> /* getopt() */
+#include <mpi.h>
+#include <pnetcdf.h>
+
+#define NY 4
+#define NX 4
+
+static int verbose;
+
+#define ERR {if(err!=NC_NOERR){printf("Error at %s:%d : %s\n", __FILE__,__LINE__, ncmpi_strerror(err));nerrs++;}}
+
+#define CHECK_MPI_ERR \
+    if (err != MPI_SUCCESS) { \
+        int errorStringLen; \
+        char errorString[MPI_MAX_ERROR_STRING]; \
+        MPI_Error_string(err, errorString, &errorStringLen); \
+        printf("Error at line %d: %s\n",__LINE__, errorString); \
+    }
+
+static void
+usage(char *argv0)
+{
+    char *help =
+    "Usage: %s [-h] | [-q] [file_name]\n"
+    "       [-h] Print help\n"
+    "       [-q] Quiet mode (reports when fail)\n"
+    "       [filename] output netCDF file name\n";
+    fprintf(stderr, help, argv0);
+}
+
+/*----< pnetcdf_check_mem_usage() >------------------------------------------*/
+/* check PnetCDF library internal memory usage */
+static int
+pnetcdf_check_mem_usage(MPI_Comm comm)
+{
+    int err, nerrs=0, rank;
+    MPI_Offset malloc_size, sum_size;
+
+    MPI_Comm_rank(comm, &rank);
+
+    /* print info about PnetCDF internal malloc usage */
+    err = ncmpi_inq_malloc_max_size(&malloc_size);
+    if (err == NC_NOERR) {
+        MPI_Reduce(&malloc_size, &sum_size, 1, MPI_OFFSET, MPI_SUM, 0, MPI_COMM_WORLD);
+        if (rank == 0 && verbose)
+            printf("maximum heap memory allocated by PnetCDF internally is %lld bytes\n",
+                   sum_size);
+
+        /* check if there is any PnetCDF internal malloc residue */
+        err = ncmpi_inq_malloc_size(&malloc_size);
+        MPI_Reduce(&malloc_size, &sum_size, 1, MPI_OFFSET, MPI_SUM, 0, MPI_COMM_WORLD);
+        if (rank == 0 && sum_size > 0)
+            printf("heap memory allocated by PnetCDF internally has %lld bytes yet to be freed\n",
+                   sum_size);
+    }
+    else if (err != NC_ENOTENABLED) {
+        printf("Error at %s:%d: %s\n", __FILE__,__LINE__,ncmpi_strerror(err));
+        nerrs++;
+    }
+    return nerrs;
+}
+
+int main(int argc, char** argv)
+{
+    extern int optind;
+    char filename[256];
+    int i, rank, nprocs, err, nerrs=0, req, status;
+    int ncid, cmode, varid, dimid[2];
+    float *buf[2];
+    MPI_Offset start[2], count[2];
+    MPI_Datatype btype;
+    int array_of_blocklengths[2];
+    MPI_Aint array_of_displacements[2];
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
+
+    verbose = 1;
+
+    /* get command-line arguments */
+    while ((i = getopt(argc, argv, "hq")) != EOF)
+        switch(i) {
+            case 'q': verbose = 0;
+                      break;
+            case 'h':
+            default:  if (rank==0) usage(argv[0]);
+                      MPI_Finalize();
+                      return 1;
+        }
+    if (argv[optind] == NULL) strcpy(filename, "testfile.nc");
+    else                      snprintf(filename, 256, "%s", argv[optind]);
+
+    if (verbose && rank == 0) printf("%s: example of using MPI_BOTTOM in flexible APIs\n",__FILE__);
+
+    /* create a new file for writing ----------------------------------------*/
+    cmode = NC_CLOBBER | NC_64BIT_DATA;
+    err = ncmpi_create(MPI_COMM_WORLD, filename, cmode, MPI_INFO_NULL, &ncid);
+    ERR
+
+    /* define dimensions */
+    err = ncmpi_def_dim(ncid, "Y", NY,        &dimid[0]); ERR
+    err = ncmpi_def_dim(ncid, "X", NX*nprocs, &dimid[1]); ERR
+
+    /* define a variable of size NY * (NX * nprocs) */
+    err = ncmpi_def_var(ncid, "var", NC_FLOAT, 2, dimid, &varid); ERR
+
+    /* exit define mode */
+    err = ncmpi_enddef(ncid); ERR
+
+    /* allocate two buffers */
+    buf[0] = (float*) malloc(sizeof(float) * NY * NX / 2);
+    buf[1] = (float*) malloc(sizeof(float) * NY * NX / 2);
+    for (i=0; i<NY*NX/2; i++) {
+        buf[0][i] = rank + 10;
+        buf[1][i] = rank + 50;
+    }
+
+    /* create a noncontiguous buffer datatype consisting 2 blocks */
+    MPI_Get_address(buf[0], &array_of_displacements[0]);
+    MPI_Get_address(buf[1], &array_of_displacements[1]);
+    array_of_blocklengths[0] = NY * NX / 2;
+    array_of_blocklengths[1] = NY * NX / 2;
+
+    err = MPI_Type_create_hindexed(2, array_of_blocklengths,
+                                   array_of_displacements,
+                                   MPI_FLOAT, &btype);
+    CHECK_MPI_ERR
+
+    err = MPI_Type_commit(&btype);
+    CHECK_MPI_ERR
+
+    start[0] = 0;
+    start[1] = NX * rank;
+    count[0] = NY;
+    count[1] = NX;
+
+    /* calling a blocking flexible API */
+    err = ncmpi_put_vara_all(ncid, varid, start, count, MPI_BOTTOM, 1, btype);
+    ERR
+
+    /* calling a blocking flexible API */
+    err = ncmpi_get_vara_all(ncid, varid, start, count, MPI_BOTTOM, 1, btype);
+    ERR
+
+    /* calling a nonblocking flexible API */
+    err = ncmpi_iput_vara(ncid, varid, start, count, MPI_BOTTOM, 1, btype, &req);
+    ERR
+
+    err = ncmpi_wait_all(ncid, 1, &req, &status); ERR
+
+    /* calling a nonblocking flexible API */
+    err = ncmpi_iget_vara(ncid, varid, start, count, MPI_BOTTOM, 1, btype, &req);
+    ERR
+
+    err = ncmpi_wait_all(ncid, 1, &req, &status); ERR
+
+    free(buf[0]);
+    free(buf[1]);
+    MPI_Type_free(&btype);
+
+    err = ncmpi_close(ncid); ERR
+
+    nerrs += pnetcdf_check_mem_usage(MPI_COMM_WORLD);
+
+    MPI_Finalize();
+    return (nerrs > 0);
+}
+
diff --git a/examples/C/vard_bottom.c b/examples/C/vard_bottom.c
new file mode 100644
index 000000000..bbeda3a58
--- /dev/null
+++ b/examples/C/vard_bottom.c
@@ -0,0 +1,339 @@
+/*********************************************************************
+ *
+ *  Copyright (C) 2024, Northwestern University and Argonne National Laboratory
+ *  See COPYRIGHT notice in top-level directory.
+ *
+ *********************************************************************/
+
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * This program is basically the same as example program vard_mvars.c, but
+ * instead of using user buffer pointer when calling the vard APIs, it
+ * constructs an MPI derived data type using absolute memory addresses and
+ * uses MPI_BOTTOM in the call to vard APIs.
+ *
+ * It shows how to use a single vard API call to write or read two
+ * consecutive variables. This example uses two MPI datatype constructors,
+ * MPI_Type_create_subarray and MPI_Type_create_hindexed, to create the same
+ * subarray view for two variables, but with different lower and upper bound
+ * MPI type maps. The two datatypes are then concatenated into a single
+ * filetype.
+ *
+ *    To compile:
+ *        mpicc -O2 vard_mvars.c -o vard_mvars -lpnetcdf
+ *
+ * Example commands for MPI run and outputs from running ncmpidump on the
+ * NetCDF file produced by this example program:
+ *
+ *  % mpiexec -n 4 ./vard_mvars /pvfs2/wkliao/testfile.nc
+ *
+ * The expected results from the output file contents are:
+ *
+ *  % ncmpidump testfile.nc
+ *    netcdf testfile {
+ *    // file format: CDF-1
+ *    dimensions:
+ *           REC_DIM = UNLIMITED ; // (2 currently)
+ *           Y = 2 ;
+ *           X = 20 ;
+ *    variables:
+ *           int fix_var0(Y, X) ;
+ *           int fix_var1(Y, X) ;
+ *           int rec_var2(REC_DIM, Y, X) ;
+ *           int rec_var3(REC_DIM, Y, X) ;
+ *    data:
+ *
+ *    fix_var0 =
+ *      0, 1, 2, 3, 4, 100, 101, 102, 103, 104, 200, 201, 202, 203, 204, 300, 301,
+ *       302, 303, 304,
+ *     10, 11, 12, 13, 14, 110, 111, 112, 113, 114, 210, 211, 212, 213, 214, 310,
+ *       311, 312, 313, 314 ;
+ *
+ *    fix_var1 =
+ *      1000, 1001, 1002, 1003, 1004, 1100, 1101, 1102, 1103, 1104, 1200, 1201,
+ *        1202, 1203, 1204, 1300, 1301, 1302, 1303, 1304,
+ *      1010, 1011, 1012, 1013, 1014, 1110, 1111, 1112, 1113, 1114, 1210, 1211,
+ *        1212, 1213, 1214, 1310, 1311, 1312, 1313, 1314 ;
+ *
+ *    rec_var2 =
+ *      _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _,
+ *      _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _,
+ *      2000, 2001, 2002, 2003, 2004, 2100, 2101, 2102, 2103, 2104, 2200, 2201,
+ *        2202, 2203, 2204, 2300, 2301, 2302, 2303, 2304,
+ *      2010, 2011, 2012, 2013, 2014, 2110, 2111, 2112, 2113, 2114, 2210, 2211,
+ *        2212, 2213, 2214, 2310, 2311, 2312, 2313, 2314 ;
+ *
+ *    rec_var3 =
+ *      _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _,
+ *      _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _,
+ *      3000, 3001, 3002, 3003, 3004, 3100, 3101, 3102, 3103, 3104, 3200, 3201,
+ *        3202, 3203, 3204, 3300, 3301, 3302, 3303, 3304,
+ *      3010, 3011, 3012, 3013, 3014, 3110, 3111, 3112, 3113, 3114, 3210, 3211,
+ *        3212, 3213, 3214, 3310, 3311, 3312, 3313, 3314 ;
+ * }
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h> /* getopt() */
+
+#include <mpi.h>
+#include <pnetcdf.h>
+
+#define NY 2
+#define NX 5
+
+static int verbose;
+
+#define ERR {if(err!=NC_NOERR){printf("Error at %s:%d : %s\n", __FILE__,__LINE__, ncmpi_strerror(err));nerrs++;}}
+
+#define CHECK_VALUE(buf,base) { \
+    for (j=0; j<NY; j++) { \
+        for (i=0; i<NX; i++) \
+            if ((buf)[j*NX+i] != (base)+rank*100+j*10+i) { \
+                printf("line %d: expecting buf[%d*NX+%d]=%d but got %d\n",\
+                       __LINE__,j,i,(base)+rank*100+j*10+i,(buf)[j*NX+i]); \
+                nerrs++; \
+            } \
+    } \
+}
+
+static void
+usage(char *argv0)
+{
+    char *help =
+    "Usage: %s [-h] | [-q] [file_name]\n"
+    "       [-h] Print help\n"
+    "       [-q] Quiet mode (reports when fail)\n"
+    "       [filename] output netCDF file name\n";
+    fprintf(stderr, help, argv0);
+}
+
+/*----< pnetcdf_check_mem_usage() >------------------------------------------*/
+/* check PnetCDF library internal memory usage */
+static int
+pnetcdf_check_mem_usage(MPI_Comm comm)
+{
+    int err, nerrs=0, rank;
+    MPI_Offset malloc_size, sum_size;
+
+    MPI_Comm_rank(comm, &rank);
+
+    /* print info about PnetCDF internal malloc usage */
+    err = ncmpi_inq_malloc_max_size(&malloc_size);
+    if (err == NC_NOERR) {
+        MPI_Reduce(&malloc_size, &sum_size, 1, MPI_OFFSET, MPI_SUM, 0, MPI_COMM_WORLD);
+        if (rank == 0 && verbose)
+            printf("maximum heap memory allocated by PnetCDF internally is %lld bytes\n",
+                   sum_size);
+
+        /* check if there is any PnetCDF internal malloc residue */
+        err = ncmpi_inq_malloc_size(&malloc_size);
+        MPI_Reduce(&malloc_size, &sum_size, 1, MPI_OFFSET, MPI_SUM, 0, MPI_COMM_WORLD);
+        if (rank == 0 && sum_size > 0)
+            printf("heap memory allocated by PnetCDF internally has %lld bytes yet to be freed\n",
+                   sum_size);
+    }
+    else if (err != NC_ENOTENABLED) {
+        printf("Error at %s:%d: %s\n", __FILE__,__LINE__,ncmpi_strerror(err));
+        nerrs++;
+    }
+    return nerrs;
+}
+
+/*----< main() >------------------------------------------------------------*/
+int main(int argc, char **argv)
+{
+    extern int optind;
+    char         filename[256];
+    int          i, j, err, ncid, varid[4], dimids[3], nerrs=0;
+    int          rank, nprocs, *buf[2];
+    int          array_of_sizes[2], array_of_subsizes[2], array_of_starts[2];
+    int          array_of_blocklengths[NY];
+    MPI_Offset   recsize, offset[2];
+    MPI_Aint     array_of_displacements[NY];
+    MPI_Datatype buftype, vtype[2], filetype;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+    verbose = 1;
+
+    /* get command-line arguments */
+    while ((i = getopt(argc, argv, "hq")) != EOF)
+        switch(i) {
+            case 'q': verbose = 0;
+                      break;
+            case 'h':
+            default:  if (rank==0) usage(argv[0]);
+                      MPI_Finalize();
+                      return 1;
+        }
+    if (argv[optind] == NULL) strcpy(filename, "testfile.nc");
+    else                      snprintf(filename, 256, "%s", argv[optind]);
+
+    MPI_Bcast(filename, 256, MPI_CHAR, 0, MPI_COMM_WORLD);
+
+    if (verbose && rank == 0) printf("%s: example of using vard APIs to write/read two variables\n",__FILE__);
+
+    buf[0] = (int*)malloc(NY * NX * sizeof(int));
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++)
+        buf[0][j*NX+i] = rank*100 + j*10 + i;
+
+    buf[1] = (int*)malloc(NY * NX * sizeof(int));
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++)
+        buf[1][j*NX+i] = 1000 + rank*100 + j*10 + i;
+
+    /* construct buftype: concatenate two separated buffers */
+    array_of_blocklengths[0] = NY*NX;
+    array_of_blocklengths[1] = NY*NX;
+    MPI_Get_address(buf[0], &array_of_displacements[0]);
+    MPI_Get_address(buf[1], &array_of_displacements[1]);
+    vtype[0] = vtype[1] = MPI_INT;
+    MPI_Type_create_struct(2, array_of_blocklengths, array_of_displacements,
+                           vtype, &buftype);
+    MPI_Type_commit(&buftype);
+
+    /* create a new NetCDF file */
+    err = ncmpi_create(MPI_COMM_WORLD, filename, NC_CLOBBER, MPI_INFO_NULL,
+                       &ncid); ERR
+
+    /* define dimensions */
+    err = ncmpi_def_dim(ncid, "REC_DIM", NC_UNLIMITED, &dimids[0]); ERR
+    err = ncmpi_def_dim(ncid, "Y",       NY,           &dimids[1]); ERR
+    err = ncmpi_def_dim(ncid, "X",       NX*nprocs,    &dimids[2]); ERR
+
+    /* define 2D fixed-size variables */
+    err = ncmpi_def_var(ncid, "fix_var0", NC_INT, 2, dimids+1, &varid[0]); ERR
+    err = ncmpi_def_var(ncid, "fix_var1", NC_INT, 2, dimids+1, &varid[1]); ERR
+    /* define 3D record variables */
+    err = ncmpi_def_var(ncid, "rec_var2", NC_INT, 3, dimids, &varid[2]); ERR
+    err = ncmpi_def_var(ncid, "rec_var3", NC_INT, 3, dimids, &varid[3]); ERR
+
+    /* enable fill mode for the two record variables */
+    err = ncmpi_def_var_fill(ncid, varid[2], 0, NULL); ERR
+    err = ncmpi_def_var_fill(ncid, varid[3], 0, NULL); ERR
+
+    err = ncmpi_enddef(ncid); ERR
+
+    /* specify the access pattern, a subarray for each variable of size
+     * NY * NX from each MPI process */
+    array_of_sizes[0]    = 2;
+    array_of_sizes[1]    = NX*nprocs;
+    array_of_subsizes[0] = NY;
+    array_of_subsizes[1] = NX;
+    array_of_starts[0]   = 0;
+    array_of_starts[1]   = NX*rank;
+
+    /* create the first datatype using MPI subarray constructor */
+    MPI_Type_create_subarray(2, array_of_sizes, array_of_subsizes,
+                             array_of_starts, MPI_ORDER_C, MPI_INT, &vtype[0]);
+    MPI_Type_commit(&vtype[0]);
+
+    /* create the second datatype using MPI hindexed constructor */
+    for (i=0; i<NY; i++) /* there are NY blocks, each of size NX */
+        array_of_blocklengths[i] = NX;
+
+    array_of_displacements[0] = NX*rank*sizeof(int);
+    for (i=1; i<NY; i++)
+        /* distance between any 2 consecutive blocks is NX*nprocs */
+        array_of_displacements[i] = array_of_displacements[i-1]
+                                  + NX*nprocs*sizeof(int);
+
+    MPI_Type_create_hindexed(NY, array_of_blocklengths, array_of_displacements,
+                             MPI_INT, &vtype[1]);
+    MPI_Type_commit(&vtype[1]);
+
+    /* concatenate two datatypes into filetype */
+    array_of_blocklengths[0] = 1;
+    array_of_blocklengths[1] = 1;
+    array_of_displacements[0] = 0;
+
+    /* calculate distance between 2 fixed-size variables */
+    err = ncmpi_inq_varoffset(ncid, varid[0], &offset[0]); ERR
+    err = ncmpi_inq_varoffset(ncid, varid[1], &offset[1]); ERR
+    array_of_displacements[1] = offset[1] - offset[0];
+
+    MPI_Type_create_struct(2, array_of_blocklengths, array_of_displacements,
+                           vtype, &filetype);
+    MPI_Type_commit(&filetype);
+
+    /* write 2 consecutive fixed-size variables in a single vard call */
+    err = ncmpi_put_vard_all(ncid, varid[0], filetype, MPI_BOTTOM, 1, buftype); ERR
+
+    /* check if the contents of write buffers are altered */
+    CHECK_VALUE(buf[0], 0)
+    CHECK_VALUE(buf[1], 1000)
+
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++) buf[0][j*NX+i] = -1;
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++) buf[1][j*NX+i] = -1;
+
+    /* read back fixed-size variables */
+    err = ncmpi_get_vard_all(ncid, varid[0], filetype, MPI_BOTTOM, 1, buftype); ERR
+
+    /* check the contents of read buffers */
+    CHECK_VALUE(buf[0], 0)
+    CHECK_VALUE(buf[1], 1000)
+
+    MPI_Type_free(&filetype);
+
+    /* obtain record size (sum of individual record of all variables) */
+    err = ncmpi_inq_recsize(ncid, &recsize); ERR
+
+    /* calculate distance between 2 record variables */
+    err = ncmpi_inq_varoffset(ncid, varid[2], &offset[0]); ERR
+    err = ncmpi_inq_varoffset(ncid, varid[3], &offset[1]); ERR
+    array_of_displacements[1] = offset[1] - offset[0];
+
+    /* fill the 1st record of two variables with fill value */
+    err = ncmpi_fill_var_rec(ncid, varid[2], 0); ERR
+    err = ncmpi_fill_var_rec(ncid, varid[3], 0); ERR
+
+    /* skip the 1st record, and write to the 2nd record of two consecutive
+     * variables */
+    array_of_displacements[0] += recsize;
+    array_of_displacements[1] += recsize;
+
+    MPI_Type_create_struct(2, array_of_blocklengths, array_of_displacements,
+                           vtype, &filetype);
+    MPI_Type_commit(&filetype);
+
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++)
+        buf[0][j*NX+i] = 2000 + rank*100 + j*10 + i;
+
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++)
+        buf[1][j*NX+i] = 3000 + rank*100 + j*10 + i;
+
+    /* write 2 consecutive record variables in a single call to vard API */
+    err = ncmpi_put_vard_all(ncid, varid[2], filetype, MPI_BOTTOM, 1, buftype); ERR
+
+    /* check if the contents of write buffers are altered */
+    CHECK_VALUE(buf[0], 2000)
+    CHECK_VALUE(buf[1], 3000)
+
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++) buf[0][j*NX+i] = -1;
+    for (j=0; j<NY; j++) for (i=0; i<NX; i++) buf[1][j*NX+i] = -1;
+
+    /* read back record variables */
+    err = ncmpi_get_vard_all(ncid, varid[2], filetype, MPI_BOTTOM, 1, buftype); ERR
+
+    /* check the contents of read buffers */
+    CHECK_VALUE(buf[0], 2000)
+    CHECK_VALUE(buf[1], 3000)
+
+    MPI_Type_free(&vtype[0]);
+    MPI_Type_free(&vtype[1]);
+    MPI_Type_free(&filetype);
+    MPI_Type_free(&buftype);
+    free(buf[0]); free(buf[1]);
+
+    err = ncmpi_close(ncid); ERR
+
+    nerrs += pnetcdf_check_mem_usage(MPI_COMM_WORLD);
+
+    MPI_Allreduce(MPI_IN_PLACE, &nerrs, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD);
+
+    MPI_Finalize();
+    return (nerrs > 0);
+}
diff --git a/examples/C/vard_mvars.c b/examples/C/vard_mvars.c
index ccb915580..caca1995d 100644
--- a/examples/C/vard_mvars.c
+++ b/examples/C/vard_mvars.c
@@ -187,7 +187,7 @@ int main(int argc, char **argv)
     array_of_displacements[0] = 0;
     MPI_Get_address(buf[0], &a0);
     MPI_Get_address(buf[1], &a1);
-    array_of_displacements[1] = a1 - a0;
+    array_of_displacements[1] = MPI_Aint_diff(a1, a0);
     vtype[0] = vtype[1] = MPI_INT;
     MPI_Type_create_struct(2, array_of_blocklengths, array_of_displacements,
                            vtype, &buftype);
diff --git a/examples/README.md b/examples/README.md
index 9f4b45904..bd1e09c89 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -70,7 +70,7 @@ with C, C++, F77, and F90 versions.
   ```
 
 * flexible_api
-  + ./C/flexible_api.c
+  + ./C/flexible_api.c ./C/flexible_bottom.c ./C/vard_bottom.c
   + ./CXX/flexible_api.cpp
   + ./F77/flexible_api.f
   + ./F90/flexible_api.f90
diff --git a/sneak_peek.md b/sneak_peek.md
index 65031f55b..812e7515d 100644
--- a/sneak_peek.md
+++ b/sneak_peek.md
@@ -60,7 +60,9 @@ This is essentially a placeholder for the next release note ...
   + none
 
 * New example programs
-  + none
+  + C/flexible_bottom.c and C/vard_bottom.c - These two examples construct MPI
+    derived data types using absolute memory addresses first and use MPI_BOTTOM
+    when calling the PnetCDF flexible APIs.
 
 * New programs for I/O benchmarks
   + none
diff --git a/src/drivers/ncmpio/ncmpio_wait.c b/src/drivers/ncmpio/ncmpio_wait.c
index 50f3b5c49..676e7ee51 100644
--- a/src/drivers/ncmpio/ncmpio_wait.c
+++ b/src/drivers/ncmpio/ncmpio_wait.c
@@ -569,7 +569,7 @@ construct_buffertypes(NC_lead_req  *lead_list,
 
         MPI_Get_address(reqs[i].xbuf, &ai);
         if (j == 0) a0 = ai;
-        disps[j] = ai - a0;
+        disps[j] = MPI_Aint_diff(ai, a0);
         j++;
     }
     /* update num_reqs to number of valid requests */
@@ -1421,7 +1421,7 @@ merge_requests(NC          *ncp,
 
         /* buf_addr is the buffer address of the first valid request */
         MPI_Get_address(reqs[i].xbuf, &addr);
-        addr -= buf_addr,  /* distance to the buf of first req */
+        addr = MPI_Aint_diff(addr, buf_addr);  /* distance to the buf of first req */
 
         ndims = lead->varp->ndims;
         if (ndims > 0) {
@@ -1478,15 +1478,15 @@ merge_requests(NC          *ncp,
 
         MPI_Offset gap = (*segs)[i].off + (*segs)[i].len - (*segs)[j].off;
         if (gap >= 0) { /* segments i and j overlaps */
-            if ((*segs)[i].buf_addr + (*segs)[i].len ==
-                (*segs)[j].buf_addr + gap) {
+            if (MPI_Aint_add((*segs)[i].buf_addr, (*segs)[i].len) ==
+                MPI_Aint_add((*segs)[j].buf_addr, gap)) {
                 /* buffers i and j are contiguous, merge j to i */
-                (*segs)[i].len += (*segs)[j].len - gap;
+                (*segs)[i].len = MPI_Aint_add((*segs)[i].len, (*segs)[j].len - gap);
             }
             else { /* buffers are not contiguous, reduce j's len */
                 (*segs)[i+1].off      = (*segs)[j].off + gap;
                 (*segs)[i+1].len      = (*segs)[j].len - gap;
-                (*segs)[i+1].buf_addr = (*segs)[j].buf_addr + gap;
+                (*segs)[i+1].buf_addr = MPI_Aint_add((*segs)[j].buf_addr, gap);
                 i++;
             }
         }
@@ -1959,7 +1959,7 @@ req_aggregation(NC     *ncp,
         if (i > 0) {
             /* get the buffer address of the first request in this group */
             MPI_Get_address(g_reqs[0].xbuf, &b_addr);
-            b_disps[i] = b_addr - b_begin; /* to 1st buffer of 1st group*/
+            b_disps[i] = MPI_Aint_diff(b_addr, b_begin); /* to 1st buffer of 1st group*/
         }
         b_blocklens[i] = 1;
     }
@@ -2374,12 +2374,12 @@ mgetput(NC     *ncp,
                 a_last_contig = a0 = ai;
                 buf = reqs[i].xbuf;
             }
-            disps[j] = ai - a0;
+            disps[j] = MPI_Aint_diff(ai, a0);
 
             req_size = blocklens[last_contig_req];
             req_size += blocklens[j];
 #ifdef HAVE_MPI_LARGE_COUNT
-            if (ai - a_last_contig == blocklens[last_contig_req]) {
+            if (MPI_Aint_diff(ai, a_last_contig) == blocklens[last_contig_req]) {
                 /* user buffer of request j is contiguous from j-1
                  * we coalesce j to j-1 */
                 blocklens[last_contig_req] += blocklens[j];
@@ -2387,7 +2387,7 @@ mgetput(NC     *ncp,
 #else
             /* if req_size overflows 4-byte int, then skip coalescing */
             if (req_size <= NC_MAX_INT &&
-                ai - a_last_contig == blocklens[last_contig_req]) {
+                MPI_Aint_diff(ai,- a_last_contig) == blocklens[last_contig_req]) {
                 /* user buffer of request j is contiguous from j-1
                  * we coalesce j to j-1 */
                 blocklens[last_contig_req] += blocklens[j];
@@ -2397,7 +2397,7 @@ mgetput(NC     *ncp,
                 /* not contiguous from request last_contig_req */
                 last_contig_req++;
                 a_last_contig = ai;
-                disps[last_contig_req] = ai - a0;
+                disps[last_contig_req] = MPI_Aint_diff(ai, a0);
                 blocklens[last_contig_req] = blocklens[i];
             }
             j++;
diff --git a/src/utils/ncvalidator/ncvalidator.c b/src/utils/ncvalidator/ncvalidator.c
index ce8c942e3..9ecb86167 100644
--- a/src/utils/ncvalidator/ncvalidator.c
+++ b/src/utils/ncvalidator/ncvalidator.c
@@ -2446,6 +2446,8 @@ val_get_NC(int fd, NC *ncp)
 
 /* End Of get NC */
 
+#ifndef BUILD_CDFDIFF
+
 /* File system types recognized by ROMIO in MPICH 4.0.0 */
 static const char* fstypes[] = {"ufs", "nfs", "xfs", "pvfs2", "gpfs", "panfs", "lustre", "daos", "testfs", "ime", "quobyte", NULL};
 
@@ -2543,7 +2545,6 @@ check_signature(char *filename)
     return NC_FORMAT_UNKNOWN;
 }
 
-#ifndef BUILD_CDFDIFF
 static void
 usage(char *argv0)
 {