diff --git a/src/inflate.c b/src/inflate.c
index 22509d73..03bee228 100644
--- a/src/inflate.c
+++ b/src/inflate.c
@@ -404,7 +404,7 @@ InflateData(mat_t *mat, z_streamp z, void *buf, unsigned int nBytes)
     if ( z->avail_in ) {
         const mat_off_t offset = -(mat_off_t)z->avail_in;
         (void)fseeko((FILE *)mat->fp, offset, SEEK_CUR);
-        bytesread -= z->avail_in;
+        /* bytesread -= z->avail_in; */
         z->avail_in = 0;
     }
 
diff --git a/src/mat.c b/src/mat.c
index 601abfc2..bf69ee39 100644
--- a/src/mat.c
+++ b/src/mat.c
@@ -639,6 +639,9 @@ Mat_Open(const char *matname, int mode)
             mat = NULL;
         }
 
+        if ( NULL == mat )
+            return mat;
+
         if ( -1 < *(hid_t *)mat->fp ) {
             H5G_info_t group_info;
             herr_t herr;
@@ -1204,9 +1207,9 @@ Mat_VarCreate(const char *name, enum matio_classes class_type, enum matio_types
             if ( matvar->isComplex ) {
                 sparse_data->data = malloc(sizeof(mat_complex_split_t));
                 if ( NULL != sparse_data->data ) {
-                    mat_complex_split_t *complex_data, *complex_data_in;
-                    complex_data = (mat_complex_split_t *)sparse_data->data;
-                    complex_data_in = (mat_complex_split_t *)sparse_data_in->data;
+                    mat_complex_split_t *complex_data = (mat_complex_split_t *)sparse_data->data;
+                    const mat_complex_split_t *complex_data_in =
+                        (mat_complex_split_t *)sparse_data_in->data;
                     complex_data->Re = malloc(sparse_data->ndata * data_size);
                     complex_data->Im = malloc(sparse_data->ndata * data_size);
                     if ( NULL != complex_data->Re )
@@ -1259,7 +1262,7 @@ Mat_CopyFile(const char *src, const char *dst)
 {
     size_t len;
     char buf[BUFSIZ] = {'\0'};
-    FILE *in = NULL;
+    FILE *in;
     FILE *out = NULL;
 
 #if defined(_WIN32)
@@ -1268,6 +1271,8 @@ Mat_CopyFile(const char *src, const char *dst)
         if ( NULL != wname ) {
             in = _wfopen(wname, L"rb");
             free(wname);
+        } else {
+            in = NULL;
         }
     }
 #else
@@ -1370,7 +1375,7 @@ Mat_VarDelete(mat_t *mat, const char *name)
                 char *new_name = strdup(mat->filename);
 #if defined(MAT73) && MAT73
                 if ( mat_file_ver == MAT_FT_MAT73 ) {
-                    err = Mat_Close73(mat);
+                    /* err = */ Mat_Close73(mat);
                 }
 #endif
                 if ( mat->fp != NULL ) {
@@ -1559,7 +1564,8 @@ Mat_VarDuplicate(const matvar_t *in, int opt)
                         out_sparse->data = malloc(sizeof(mat_complex_split_t));
                         if ( out_sparse->data != NULL ) {
                             mat_complex_split_t *out_data = (mat_complex_split_t *)out_sparse->data;
-                            mat_complex_split_t *in_data = (mat_complex_split_t *)in_sparse->data;
+                            const mat_complex_split_t *in_data =
+                                (mat_complex_split_t *)in_sparse->data;
                             out_data->Re = malloc(in_sparse->ndata * Mat_SizeOf(in->data_type));
                             if ( NULL != out_data->Re )
                                 memcpy(out_data->Re, in_data->Re,
@@ -1580,7 +1586,7 @@ Mat_VarDuplicate(const matvar_t *in, int opt)
                 out->internal->data = malloc(sizeof(mat_complex_split_t));
                 if ( out->internal->data != NULL ) {
                     mat_complex_split_t *out_data = (mat_complex_split_t *)out->internal->data;
-                    mat_complex_split_t *in_data = (mat_complex_split_t *)in->internal->data;
+                    const mat_complex_split_t *in_data = (mat_complex_split_t *)in->internal->data;
                     out_data->Re = malloc(out->nbytes);
                     if ( NULL != out_data->Re )
                         memcpy(out_data->Re, in_data->Re, out->nbytes);
@@ -2465,7 +2471,8 @@ Mat_VarPrint(const matvar_t *matvar, int printdata)
  * @retval 0 on success
  */
 int
-Mat_VarReadData(mat_t *mat, matvar_t *matvar, void *data, int *start, int *stride, int *edge)
+Mat_VarReadData(mat_t *mat, matvar_t *matvar, void *data, const int *start, const int *stride,
+                const int *edge)
 {
     int err = MATIO_E_NO_ERROR;
 
@@ -2842,7 +2849,7 @@ Mat_VarReadNextPredicate(mat_t *mat, mat_iter_pred_t pred, const void *user_data
  * @see Mat_VarWrite/Mat_VarWriteAppend
  */
 int
-Mat_VarWriteInfo(mat_t *mat, matvar_t *matvar)
+Mat_VarWriteInfo(const mat_t *mat, matvar_t *matvar)
 {
     Mat_Critical(
         "Mat_VarWriteInfo/Mat_VarWriteData is not supported. "
@@ -2867,8 +2874,8 @@ Mat_VarWriteInfo(mat_t *mat, matvar_t *matvar)
  * @see Mat_VarWrite/Mat_VarWriteAppend
  */
 int
-Mat_VarWriteData(mat_t *mat, matvar_t *matvar, void *data, const int *start, const int *stride,
-                 const int *edge)
+Mat_VarWriteData(const mat_t *mat, matvar_t *matvar, void *data, const int *start,
+                 const int *stride, const int *edge)
 {
     Mat_Critical(
         "Mat_VarWriteInfo/Mat_VarWriteData is not supported. "
diff --git a/src/mat4.c b/src/mat4.c
index 583294a8..9aee2a33 100644
--- a/src/mat4.c
+++ b/src/mat4.c
@@ -56,7 +56,7 @@
 mat_t *
 Mat_Create4(const char *matname)
 {
-    FILE *fp = NULL;
+    FILE *fp;
     mat_t *mat = NULL;
 
 #if defined(_WIN32)
@@ -64,6 +64,8 @@ Mat_Create4(const char *matname)
     if ( NULL != wname ) {
         fp = _wfopen(wname, L"w+b");
         free(wname);
+    } else {
+        fp = NULL;
     }
 #else
     fp = fopen(matname, "w+b");
@@ -119,7 +121,6 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
         mat_int32_t namelen;
     } Fmatrix;
 
-    mat_uint32_t i;
     Fmatrix x;
 
     if ( NULL == mat || NULL == matvar )
@@ -200,9 +201,7 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
             fwrite(&x, sizeof(Fmatrix), 1, (FILE *)mat->fp);
             fwrite(matvar->name, sizeof(char), x.namelen, (FILE *)mat->fp);
             if ( matvar->isComplex ) {
-                mat_complex_split_t *complex_data;
-
-                complex_data = (mat_complex_split_t *)matvar->data;
+                const mat_complex_split_t *complex_data = (mat_complex_split_t *)matvar->data;
                 fwrite(complex_data->Re, matvar->data_size, nelems, (FILE *)mat->fp);
                 fwrite(complex_data->Im, matvar->data_size, nelems, (FILE *)mat->fp);
             } else {
@@ -213,7 +212,7 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
         case MAT_C_SPARSE: {
             mat_sparse_t *sparse;
             double tmp;
-            mat_uint32_t j;
+            mat_uint32_t i, j;
             size_t stride = Mat_SizeOf(matvar->data_type);
 #if !defined(EXTENDED_SPARSE)
             if ( MAT_T_DOUBLE != matvar->data_type )
@@ -247,12 +246,9 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
             fwrite(&tmp, sizeof(double), 1, (FILE *)mat->fp);
             tmp = 0.;
             if ( matvar->isComplex ) {
-                mat_complex_split_t *complex_data;
-                char *re, *im;
-
-                complex_data = (mat_complex_split_t *)sparse->data;
-                re = (char *)complex_data->Re;
-                im = (char *)complex_data->Im;
+                mat_complex_split_t *complex_data = (mat_complex_split_t *)sparse->data;
+                const char *re = (char *)complex_data->Re;
+                const char *im = (char *)complex_data->Im;
                 for ( i = 0; i < sparse->njc - 1; i++ ) {
                     for ( j = sparse->jc[i]; j < sparse->jc[i + 1] && j < sparse->ndata; j++ ) {
                         fwrite(re + j * stride, stride, 1, (FILE *)mat->fp);
@@ -265,7 +261,7 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
                     }
                 }
             } else {
-                char *data = (char *)sparse->data;
+                const char *data = (char *)sparse->data;
                 for ( i = 0; i < sparse->njc - 1; i++ ) {
                     for ( j = sparse->jc[i]; j < sparse->jc[i + 1] && j < sparse->ndata; j++ ) {
                         fwrite(data + j * stride, stride, 1, (FILE *)mat->fp);
@@ -768,8 +764,8 @@ Mat_VarRead4(mat_t *mat, matvar_t *matvar)
  * @endif
  */
 int
-Mat_VarReadData4(mat_t *mat, matvar_t *matvar, void *data, const int *start, const int *stride,
-                 const int *edge)
+Mat_VarReadData4(mat_t *mat, const matvar_t *matvar, void *data, const int *start,
+                 const int *stride, const int *edge)
 {
     int err = MATIO_E_NO_ERROR;
 
diff --git a/src/mat4.h b/src/mat4.h
index 7455bcf5..1e81b41a 100644
--- a/src/mat4.h
+++ b/src/mat4.h
@@ -38,7 +38,7 @@ EXTERN mat_t *Mat_Create4(const char *matname);
 
 EXTERN int Mat_VarWrite4(mat_t *mat, const matvar_t *matvar);
 EXTERN int Mat_VarRead4(mat_t *mat, matvar_t *matvar);
-EXTERN int Mat_VarReadData4(mat_t *mat, matvar_t *matvar, void *data, const int *start,
+EXTERN int Mat_VarReadData4(mat_t *mat, const matvar_t *matvar, void *data, const int *start,
                             const int *stride, const int *edge);
 EXTERN int Mat_VarReadDataLinear4(mat_t *mat, matvar_t *matvar, void *data, int start, int stride,
                                   int edge);
diff --git a/src/mat5.c b/src/mat5.c
index 801e8012..8f208168 100644
--- a/src/mat5.c
+++ b/src/mat5.c
@@ -65,7 +65,7 @@ static mat_complex_split_t null_complex_data = {NULL, NULL};
 static int GetTypeBufSize(matvar_t *matvar, size_t *size);
 static int GetStructFieldBufSize(matvar_t *matvar, size_t *size);
 static int GetCellArrayFieldBufSize(matvar_t *matvar, size_t *size);
-static void SetFieldNames(matvar_t *matvar, char *buf, size_t nfields,
+static void SetFieldNames(matvar_t *matvar, const char *buf, size_t nfields,
                           mat_uint32_t fieldname_length);
 static size_t ReadSparse(mat_t *mat, const matvar_t *matvar, mat_uint32_t *n, mat_uint32_t **v);
 #if HAVE_ZLIB
@@ -457,7 +457,7 @@ GetEmptyMatrixMaxBufSize(const char *name, int rank, size_t *size)
 }
 
 static void
-SetFieldNames(matvar_t *matvar, char *buf, size_t nfields, mat_uint32_t fieldname_length)
+SetFieldNames(matvar_t *matvar, const char *buf, size_t nfields, mat_uint32_t fieldname_length)
 {
     matvar->internal->num_fields = nfields;
     matvar->internal->fieldnames = (char **)calloc(nfields, sizeof(*matvar->internal->fieldnames));
@@ -479,12 +479,12 @@ ReadSparse(mat_t *mat, const matvar_t *matvar, mat_uint32_t *n, mat_uint32_t **v
 {
     int data_in_tag = 0;
     enum matio_types packed_type;
-    mat_uint32_t tag[2] = {0, 0};
     size_t bytesread = 0;
     mat_uint32_t N = 0;
 
     if ( matvar->compression == MAT_COMPRESSION_ZLIB ) {
 #if HAVE_ZLIB
+        mat_uint32_t tag[2] = {0, 0};
         matvar->internal->z->avail_in = 0;
         if ( 0 != Inflate(mat, matvar->internal->z, tag, 4, &bytesread) ) {
             return bytesread;
@@ -501,6 +501,7 @@ ReadSparse(mat_t *mat, const matvar_t *matvar, mat_uint32_t *n, mat_uint32_t **v
         }
 #endif
     } else {
+        mat_uint32_t tag[2] = {0, 0};
         if ( 0 != Read(tag, 4, 1, (FILE *)mat->fp, &bytesread) ) {
             return bytesread;
         }
@@ -524,9 +525,8 @@ ReadSparse(mat_t *mat, const matvar_t *matvar, mat_uint32_t *n, mat_uint32_t **v
     *n = N / 4;
     *v = (mat_uint32_t *)calloc(N, 1);
     if ( NULL != *v ) {
-        int nBytes;
         if ( matvar->compression == MAT_COMPRESSION_NONE ) {
-            nBytes = ReadUInt32Data(mat, *v, packed_type, *n);
+            int nBytes = ReadUInt32Data(mat, *v, packed_type, *n);
             /*
                 * If the data was in the tag we started on a 4-byte
                 * boundary so add 4 to make it an 8-byte
@@ -538,7 +538,7 @@ ReadSparse(mat_t *mat, const matvar_t *matvar, mat_uint32_t *n, mat_uint32_t **v
                 (void)fseeko((FILE *)mat->fp, 8 - (nBytes % 8), SEEK_CUR);
 #if HAVE_ZLIB
         } else if ( matvar->compression == MAT_COMPRESSION_ZLIB ) {
-            nBytes = ReadCompressedUInt32Data(mat, matvar->internal->z, *v, packed_type, *n);
+            int nBytes = ReadCompressedUInt32Data(mat, matvar->internal->z, *v, packed_type, *n);
             /*
                 * If the data was in the tag we started on a 4-byte
                 * boundary so add 4 to make it an 8-byte
@@ -629,7 +629,7 @@ GetMatrixMaxBufSize(matvar_t *matvar, size_t *size)
 mat_t *
 Mat_Create5(const char *matname, const char *hdr_str)
 {
-    FILE *fp = NULL;
+    FILE *fp;
     mat_int16_t endian = 0, version;
     mat_t *mat = NULL;
     size_t err;
@@ -640,6 +640,8 @@ Mat_Create5(const char *matname, const char *hdr_str)
     if ( NULL != wname ) {
         fp = _wfopen(wname, L"w+b");
         free(wname);
+    } else {
+        fp = NULL;
     }
 #else
     fp = fopen(matname, "w+b");
@@ -984,7 +986,7 @@ WriteCompressedData(mat_t *mat, z_streamp z, void *data, int N, enum matio_types
 static size_t
 ReadNextCell(mat_t *mat, matvar_t *matvar)
 {
-    size_t bytesread = 0, i;
+    size_t bytesread = 0;
     int err;
     matvar_t **cells = NULL;
     size_t nelems = 1;
@@ -1011,6 +1013,7 @@ ReadNextCell(mat_t *mat, matvar_t *matvar)
 
     if ( matvar->compression == MAT_COMPRESSION_ZLIB ) {
 #if HAVE_ZLIB
+        size_t i;
         mat_uint32_t uncomp_buf[16];
         mat_uint32_t nBytes;
         mat_uint32_t array_flags;
@@ -1233,6 +1236,7 @@ ReadNextCell(mat_t *mat, matvar_t *matvar)
 #endif
 
     } else {
+        size_t i;
         mat_uint32_t buf[6] = {0, 0, 0, 0, 0, 0};
         mat_uint32_t nBytes;
         mat_uint32_t array_flags;
@@ -1329,11 +1333,10 @@ ReadNextCell(mat_t *mat, matvar_t *matvar)
                 (void)Mat_uint32Swap(buf);
                 (void)Mat_uint32Swap(buf + 1);
             }
-            name_len = 0;
             if ( buf[1] > 0 ) {
                 /* Name of variable */
                 if ( buf[0] == MAT_T_INT8 ) { /* Name not in tag */
-                    name_len = buf[1];
+                    mat_uint32_t name_len = buf[1];
                     if ( name_len % 8 > 0 ) {
                         if ( name_len < UINT32_MAX - 8 + (name_len % 8) ) {
                             name_len = name_len + 8 - (name_len % 8);
@@ -1375,9 +1378,8 @@ ReadNextCell(mat_t *mat, matvar_t *matvar)
 static size_t
 ReadNextStructField(mat_t *mat, matvar_t *matvar)
 {
-    mat_uint32_t fieldname_size;
     int err;
-    size_t bytesread = 0, nfields, i;
+    size_t bytesread = 0;
     matvar_t **fields = NULL;
     size_t nelems = 1, nelems_x_nfields;
 
@@ -1388,8 +1390,9 @@ ReadNextStructField(mat_t *mat, matvar_t *matvar)
     }
     if ( matvar->compression == MAT_COMPRESSION_ZLIB ) {
 #if HAVE_ZLIB
+        size_t nfields, i;
         mat_uint32_t uncomp_buf[16];
-        mat_uint32_t array_flags, len;
+        mat_uint32_t array_flags, len, fieldname_size;
 
         memset(&uncomp_buf, 0, sizeof(uncomp_buf));
         /* Field name length */
@@ -1633,7 +1636,7 @@ ReadNextStructField(mat_t *mat, matvar_t *matvar)
                             else if ( nBytes <= (1 << MAX_WBITS) ) {
                                 /* Memory optimization: Read data if less in size
                                    than the zlib inflate state (approximately) */
-                                err = Mat_VarRead5(mat, fields[i]);
+                                /* err = */ Mat_VarRead5(mat, fields[i]);
                                 fields[i]->internal->data = fields[i]->data;
                                 fields[i]->data = NULL;
                             }
@@ -1662,8 +1665,9 @@ ReadNextStructField(mat_t *mat, matvar_t *matvar)
         Mat_Critical("Not compiled with zlib support");
 #endif
     } else {
+        size_t nfields, i;
         mat_uint32_t buf[6] = {0, 0, 0, 0, 0, 0};
-        mat_uint32_t array_flags, len;
+        mat_uint32_t array_flags, len, fieldname_size;
 
         err = Read(buf, 4, 2, (FILE *)mat->fp, &bytesread);
         if ( err ) {
@@ -2000,7 +2004,7 @@ WriteType(mat_t *mat, matvar_t *matvar)
         case MAT_C_INT8:
         case MAT_C_UINT8: {
             if ( matvar->isComplex ) {
-                mat_complex_split_t *complex_data = (mat_complex_split_t *)matvar->data;
+                const mat_complex_split_t *complex_data = (mat_complex_split_t *)matvar->data;
 
                 if ( NULL == matvar->data )
                     complex_data = &null_complex_data;
@@ -2025,7 +2029,7 @@ WriteType(mat_t *mat, matvar_t *matvar)
             if ( matvar->data_type == MAT_T_UTF8 ) {
                 nelems = matvar->nbytes;
             }
-            nBytes = WriteCharData(mat, matvar->data, nelems, matvar->data_type);
+            /* nBytes = */ WriteCharData(mat, matvar->data, nelems, matvar->data_type);
             break;
         case MAT_C_CELL: {
             size_t i;
@@ -2844,8 +2848,8 @@ Mat_WriteCompressedEmptyVariable5(mat_t *mat, const char *name, int rank, const
         memset(uncomp_buf, 0, 8);
         uncomp_buf[0] = (array_name_len << 16) | array_name_type;
         memcpy(uncomp_buf + 1, name, array_name_len);
-        if ( array_name_len % 4 )
-            array_name_len += 4 - (array_name_len % 4);
+        /* if ( array_name_len % 4 ) */
+        /*    array_name_len += 4 - (array_name_len % 4); */
 
         z->next_in = ZLIB_BYTE_PTR(uncomp_buf);
         z->avail_in = 8;
@@ -4888,7 +4892,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
     int array_flags_type = MAT_T_UINT32, dims_array_type = MAT_T_INT32;
     int array_flags_size = 8, matrix_type = MAT_T_MATRIX;
     const mat_uint32_t pad4 = 0;
-    int nBytes, i, nzmax = 0;
+    int nBytes, nzmax = 0;
     mat_off_t start = 0, end = 0;
 
     if ( NULL == mat )
@@ -4905,6 +4909,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
 #else
     {
 #endif
+        int i;
         fwrite(&matrix_type, 4, 1, (FILE *)mat->fp);
         fwrite(&pad4, 4, 1, (FILE *)mat->fp);
         start = ftello((FILE *)mat->fp);
@@ -4973,8 +4978,8 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
     } else if ( compress == MAT_COMPRESSION_ZLIB ) {
         mat_uint32_t comp_buf[512];
         mat_uint32_t uncomp_buf[512];
-        int buf_size = 512, err;
-        size_t byteswritten = 0, matrix_max_buf_size;
+        int buf_size = 512, err, i;
+        size_t matrix_max_buf_size;
         z_streamp z;
 
         z = (z_streamp)calloc(1, sizeof(*z));
@@ -5021,8 +5026,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
             z->next_out = ZLIB_BYTE_PTR(comp_buf);
             z->avail_out = buf_size * sizeof(*comp_buf);
             deflate(z, Z_NO_FLUSH);
-            byteswritten +=
-                fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
+            fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
         } while ( z->avail_out == 0 );
         uncomp_buf[0] = array_flags_type;
         uncomp_buf[1] = array_flags_size;
@@ -5048,8 +5052,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
             z->next_out = ZLIB_BYTE_PTR(comp_buf);
             z->avail_out = buf_size * sizeof(*comp_buf);
             deflate(z, Z_NO_FLUSH);
-            byteswritten +=
-                fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
+            fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
         } while ( z->avail_out == 0 );
         /* Name of variable */
         if ( strlen(matvar->name) <= 4 ) {
@@ -5059,8 +5062,8 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
             memset(uncomp_buf, 0, 8);
             uncomp_buf[0] = (array_name_len << 16) | array_name_type;
             memcpy(uncomp_buf + 1, matvar->name, array_name_len);
-            if ( array_name_len % 4 )
-                array_name_len += 4 - (array_name_len % 4);
+            /* if ( array_name_len % 4 ) */
+            /*     array_name_len += 4 - (array_name_len % 4); */
 
             z->next_in = ZLIB_BYTE_PTR(uncomp_buf);
             z->avail_in = 8;
@@ -5068,8 +5071,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
                 z->next_out = ZLIB_BYTE_PTR(comp_buf);
                 z->avail_out = buf_size * sizeof(*comp_buf);
                 deflate(z, Z_NO_FLUSH);
-                byteswritten += fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out,
-                                       (FILE *)mat->fp);
+                fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
             } while ( z->avail_out == 0 );
         } else {
             mat_uint32_t array_name_len = (mat_uint32_t)strlen(matvar->name);
@@ -5087,8 +5089,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
                 z->next_out = ZLIB_BYTE_PTR(comp_buf);
                 z->avail_out = buf_size * sizeof(*comp_buf);
                 deflate(z, Z_NO_FLUSH);
-                byteswritten += fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out,
-                                       (FILE *)mat->fp);
+                fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
             } while ( z->avail_out == 0 );
         }
         if ( NULL != matvar->internal ) {
@@ -5109,8 +5110,7 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
             z->next_out = ZLIB_BYTE_PTR(comp_buf);
             z->avail_out = buf_size * sizeof(*comp_buf);
             err = deflate(z, Z_FINISH);
-            byteswritten +=
-                fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
+            fwrite(comp_buf, 1, buf_size * sizeof(*comp_buf) - z->avail_out, (FILE *)mat->fp);
         } while ( err != Z_STREAM_END && z->avail_out == 0 );
 #if 0
         if ( byteswritten % 8 )
@@ -5146,7 +5146,7 @@ matvar_t *
 Mat_VarReadNextInfo5(mat_t *mat)
 {
     int err;
-    mat_uint32_t data_type, array_flags, nBytes;
+    mat_uint32_t data_type, nBytes;
     mat_off_t fpos;
     matvar_t *matvar = NULL;
 
@@ -5178,7 +5178,6 @@ Mat_VarReadNextInfo5(mat_t *mat)
         case MAT_T_COMPRESSED: {
 #if HAVE_ZLIB
             mat_uint32_t uncomp_buf[16];
-            int nbytes;
             size_t bytesread = 0;
 
             memset(&uncomp_buf, 0, sizeof(uncomp_buf));
@@ -5200,11 +5199,15 @@ Mat_VarReadNextInfo5(mat_t *mat)
 
             /* Read variable tag */
             err = Inflate(mat, matvar->internal->z, uncomp_buf, 8, &bytesread);
+            if ( err ) {
+                Mat_VarFree(matvar);
+                matvar = NULL;
+                break;
+            }
             if ( mat->byteswap ) {
                 (void)Mat_uint32Swap(uncomp_buf);
                 (void)Mat_uint32Swap(uncomp_buf + 1);
             }
-            nbytes = uncomp_buf[1];
             if ( uncomp_buf[0] != MAT_T_MATRIX ) {
                 (void)fseeko((FILE *)mat->fp, (mat_off_t)(nBytes - bytesread), SEEK_CUR);
                 Mat_VarFree(matvar);
@@ -5226,7 +5229,7 @@ Mat_VarReadNextInfo5(mat_t *mat)
             }
             /* Array flags */
             if ( uncomp_buf[0] == MAT_T_UINT32 ) {
-                array_flags = uncomp_buf[2];
+                mat_uint32_t array_flags = uncomp_buf[2];
                 matvar->class_type = CLASS_FROM_ARRAY_FLAGS(array_flags);
                 matvar->isComplex = (array_flags & MAT_F_COMPLEX);
                 matvar->isGlobal = (array_flags & MAT_F_GLOBAL);
@@ -5262,7 +5265,7 @@ Mat_VarReadNextInfo5(mat_t *mat)
                 if ( uncomp_buf[0] == MAT_T_INT32 ) {
                     int j;
                     size_t size;
-                    nbytes = uncomp_buf[1];
+                    int nbytes = uncomp_buf[1];
                     matvar->rank = nbytes / 4;
                     if ( 0 == do_clean && matvar->rank > 13 ) {
                         int rank = matvar->rank;
@@ -5397,7 +5400,7 @@ Mat_VarReadNextInfo5(mat_t *mat)
 
             /* Array flags */
             if ( buf[0] == MAT_T_UINT32 || buf[0] == MAT_T_INT32 ) { /* Also allow INT32 for SWAN */
-                array_flags = buf[2];
+                mat_uint32_t array_flags = buf[2];
                 matvar->class_type = CLASS_FROM_ARRAY_FLAGS(array_flags);
                 matvar->isComplex = (array_flags & MAT_F_COMPLEX);
                 matvar->isGlobal = (array_flags & MAT_F_GLOBAL);
diff --git a/src/matio.h b/src/matio.h
index 06d877eb..8a805258 100644
--- a/src/matio.h
+++ b/src/matio.h
@@ -331,8 +331,8 @@ EXTERN matvar_t *Mat_VarGetStructsLinear(const matvar_t *matvar, int start, int
                                          int copy_fields);
 EXTERN void Mat_VarPrint(const matvar_t *matvar, int printdata);
 EXTERN matvar_t *Mat_VarRead(mat_t *mat, const char *name);
-EXTERN int Mat_VarReadData(mat_t *mat, matvar_t *matvar, void *data, int *start, int *stride,
-                           int *edge);
+EXTERN int Mat_VarReadData(mat_t *mat, matvar_t *matvar, void *data, const int *start,
+                           const int *stride, const int *edge);
 EXTERN int Mat_VarReadDataAll(mat_t *mat, matvar_t *matvar);
 EXTERN int Mat_VarReadDataLinear(mat_t *mat, matvar_t *matvar, void *data, int start, int stride,
                                  int edge);
@@ -350,8 +350,8 @@ EXTERN matvar_t *Mat_VarSetStructFieldByName(matvar_t *matvar, const char *field
 EXTERN int Mat_VarWrite(mat_t *mat, matvar_t *matvar, enum matio_compression compress);
 EXTERN int Mat_VarWriteAppend(mat_t *mat, matvar_t *matvar, enum matio_compression compress,
                               int dim);
-EXTERN int Mat_VarWriteInfo(mat_t *mat, matvar_t *matvar);
-EXTERN int Mat_VarWriteData(mat_t *mat, matvar_t *matvar, void *data, const int *start,
+EXTERN int Mat_VarWriteInfo(const mat_t *mat, matvar_t *matvar);
+EXTERN int Mat_VarWriteData(const mat_t *mat, matvar_t *matvar, void *data, const int *start,
                             const int *stride, const int *edge);
 
 /* Other functions */
diff --git a/test/test_snprintf.c b/test/test_snprintf.c
index 704bd9d9..818da896 100644
--- a/test/test_snprintf.c
+++ b/test/test_snprintf.c
@@ -15,7 +15,7 @@ int main(int argc, char **argv)
 {
         char buf1[1024];
         char buf2[1024];
-        char *fp_fmt[] = {
+        const char *fp_fmt[] = {
                 "%1.1f",
                 "%-1.5f",
                 "%1.5f",
@@ -33,10 +33,10 @@ int main(int argc, char **argv)
                 "-16.16f",
                 NULL
         };
-        double fp_nums[] = { 6442452944.1234, -1.5, 134.21, 91340.2, 341.1234, 203.9, 0.96, 0.996,
+        const double fp_nums[] = { 6442452944.1234, -1.5, 134.21, 91340.2, 341.1234, 203.9, 0.96, 0.996,
                              0.9996, 1.996, 4.136, 5.030201, 0.00205,
                              /* END LIST */ 0};
-        char *int_fmt[] = {
+        const char *int_fmt[] = {
                 "%-1.5d",
                 "%1.5d",
                 "%123.9d",
@@ -49,8 +49,8 @@ int main(int argc, char **argv)
                 "%d",
                 NULL
         };
-        long int_nums[] = { -1, 134, 91340, 341, 0203, 0};
-        char *str_fmt[] = {
+        const long int_nums[] = { -1, 134, 91340, 341, 0203, 0};
+        const char *str_fmt[] = {
                 "10.5s",
                 "5.10s",
                 "10.1s",
@@ -63,7 +63,7 @@ int main(int argc, char **argv)
                 "%10s",
                 NULL
         };
-        char *str_vals[] = {"hello", "a", "", "a longer string", NULL};
+        const char *str_vals[] = {"hello", "a", "", "a longer string", NULL};
         int x, y;
         int fail = 0;
         int num = 0;