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Improvement: Use a fixed constant for the length of the description field in t8_vtk_data_field_t #2499

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Improvement: Use a fixed constant for the length of the description field in t8_vtk_data_field_t #2499

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1a9f2ce
introduce a fixed constant for the length of the description field
benegee Oct 7, 2026
3766dd1
change BUFSIZ to T8_VTK_MAX_STRING_LENGTH
benegee Oct 7, 2026
3dd3d35
fmt
benegee Oct 8, 2026
baf2f13
Merge branch 'main' into bg/fixed-vtk-description-string-length
holke Oct 8, 2026
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2 changes: 1 addition & 1 deletion example/IO/cmesh/vtk/t8_cmesh_read_from_vtk.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,7 @@ t8_forest_construct_from_vtk (const char *prefix, sc_MPI_Comm comm, const int va
vtk_data[ivalues].data = cell_values[ivalues];
/*TODO: Arbitrary type of data */
vtk_data[ivalues].type = T8_VTK_SCALAR;
snprintf (vtk_data[ivalues].description, BUFSIZ, "cell_data_%i", ivalues);
snprintf (vtk_data[ivalues].description, T8_VTK_MAX_STRING_LENGTH, "cell_data_%i", ivalues);
}

for (t8_locidx_t itree = 0; itree < num_trees; itree++) {
Expand Down
8 changes: 4 additions & 4 deletions example/advect/t8_advection.cxx
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Expand Up @@ -1112,16 +1112,16 @@ t8_advect_write_vtk (t8_advect_problem_t *problem)
}

/* Write meta data for vtk */
snprintf (vtk_data[0].description, BUFSIZ, "Num. Solution");
snprintf (vtk_data[0].description, T8_VTK_MAX_STRING_LENGTH, "Num. Solution");
vtk_data[0].type = T8_VTK_SCALAR;
vtk_data[0].data = u_and_phi_array[0];
snprintf (vtk_data[1].description, BUFSIZ, "Ana. Solution");
snprintf (vtk_data[1].description, T8_VTK_MAX_STRING_LENGTH, "Ana. Solution");
vtk_data[1].type = T8_VTK_SCALAR;
vtk_data[1].data = u_and_phi_array[1];
snprintf (vtk_data[2].description, BUFSIZ, "Error");
snprintf (vtk_data[2].description, T8_VTK_MAX_STRING_LENGTH, "Error");
vtk_data[2].type = T8_VTK_SCALAR;
vtk_data[2].data = u_and_phi_array[2];
snprintf (vtk_data[3].description, BUFSIZ, "Flow");
snprintf (vtk_data[3].description, T8_VTK_MAX_STRING_LENGTH, "Flow");
vtk_data[3].type = T8_VTK_VECTOR;
vtk_data[3].data = u_and_phi_array[3];
/* Write filename */
Expand Down
2 changes: 1 addition & 1 deletion example/remove/t8_example_gauss_blob.cxx
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Expand Up @@ -79,7 +79,7 @@ t8_output_data_to_vtu (t8_forest_t forest, double *data, const char *prefix)
{
t8_vtk_data_field_t vtk_data;
vtk_data.type = T8_VTK_SCALAR;
snprintf (vtk_data.description, BUFSIZ, "Gauss");
snprintf (vtk_data.description, T8_VTK_MAX_STRING_LENGTH, "Gauss");
vtk_data.data = data;

int num_data = 1;
Expand Down
52 changes: 28 additions & 24 deletions src/t8_vtk/t8_vtk.c
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Expand Up @@ -71,21 +71,22 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra

if (num_data > 0) {
/* Print point data for data fields */
char vtkPointDataString[BUFSIZ] = "";
char vtkPointVectorString[BUFSIZ] = "";
char description[BUFSIZ];
char vtkPointDataString[T8_VTK_MAX_STRING_LENGTH] = "";
char vtkPointVectorString[T8_VTK_MAX_STRING_LENGTH] = "";
char description[T8_VTK_MAX_STRING_LENGTH];

for (idata = 0; idata < num_data && data[idata].type == T8_VTK_SCALAR; idata++) {
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
/* Note: gcc >= 7.1 prints a warning if we
* do not check the return value of snprintf. */
t8_debugf ("Warning: Truncated vtk point data description to '%s'\n", description);
}

printed += snprintf (vtkPointDataString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "", description);
printed += snprintf (vtkPointDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", description);
}
num_scalars = idata;
/* Write Vector fields in data */
Expand All @@ -94,16 +95,16 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra
for (idata = num_scalars; idata < num_data; idata++) {
SC_CHECK_ABORT (data[idata].type == T8_VTK_VECTOR, "vtk data mismatch. After scalar fields only vector"
" fields are allowed.");
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
/* Note: gcc >= 7.1 prints a warning if we
* do not check the return value of snprintf. */
t8_debugf ("Warning: Truncated vtk point data description to '%s'\n", description);
}
printed
+= snprintf (vtkPointVectorString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "", description);
printed += snprintf (vtkPointVectorString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", description);
}
}

Expand All @@ -118,9 +119,9 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra
}
/* Write data fields */
for (idata = 0; idata < num_scalars; idata++) {
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
/* Note: gcc >= 7.1 prints a warning if we
* do not check the return value of snprintf. */
Expand All @@ -136,9 +137,9 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra
/* Write vector data fields */
for (idata = num_scalars; idata < num_data; idata++) {
T8_ASSERT (data[idata].type == T8_VTK_VECTOR);
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
/* Note: gcc >= 7.1 prints a warning if we
* do not check the return value of snprintf. */
Expand All @@ -157,24 +158,27 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra
/* reset counter */
printed = 0;
if (write_cell_data) {
char vtkCellDataString[BUFSIZ] = "";
char vtkCellVectorString[BUFSIZ] = "";
char vtkCellDataString[T8_VTK_MAX_STRING_LENGTH] = "";
char vtkCellVectorString[T8_VTK_MAX_STRING_LENGTH] = "";

if (write_tree) {
printed += snprintf (vtkCellDataString + printed, BUFSIZ - printed, "treeid");
printed += snprintf (vtkCellDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "treeid");
}
if (write_rank) {
printed += snprintf (vtkCellDataString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "", "mpirank");
printed += snprintf (vtkCellDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", "mpirank");
}
if (write_level) {
printed += snprintf (vtkCellDataString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "", "level");
printed += snprintf (vtkCellDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", "level");
}
if (write_id) {
printed += snprintf (vtkCellDataString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "", "element_id");
printed += snprintf (vtkCellDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", "element_id");
}
for (idata = 0; idata < num_data && data[idata].type == T8_VTK_SCALAR; idata++) {
printed += snprintf (vtkCellDataString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "",
data[idata].description);
printed += snprintf (vtkCellDataString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", data[idata].description);
}
num_scalars = idata;
/* Write Vector fields in data */
Expand All @@ -183,8 +187,8 @@ t8_write_pvtu (const char *filename, int num_procs, int write_tree, int write_ra
for (idata = num_scalars; idata < num_data; idata++) {
SC_CHECK_ABORT (data[idata].type == T8_VTK_VECTOR, "vtk data mismatch. After scalar fields only vector"
" fields are allowed.");
printed += snprintf (vtkCellVectorString + printed, BUFSIZ - printed, "%s%s", printed > 0 ? "," : "",
data[idata].description);
printed += snprintf (vtkCellVectorString + printed, T8_VTK_MAX_STRING_LENGTH - printed, "%s%s",
printed > 0 ? "," : "", data[idata].description);
}
}
if (strcmp (vtkCellDataString, "")) {
Expand Down
7 changes: 4 additions & 3 deletions src/t8_vtk/t8_vtk.h
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Expand Up @@ -46,7 +46,8 @@
#define T8_VTK_FLOAT_TYPE double
#endif

#define T8_VTK_FORMAT_STRING "ascii" /**< Format string for vtk */
#define T8_VTK_FORMAT_STRING "ascii" /**< Format string for vtk */
#define T8_VTK_MAX_STRING_LENGTH 1023 /**< Maximal string length for the description in t8_vtk_data_field_t */

@holke holke Oct 8, 2026

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Could you please add a comment in the code why we choose 1023 - since its a magic number, we should have an explanation for it.

@benegee benegee Oct 8, 2026

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Embarrassing...

It had been 1024. 1K, just because I like the number, and I thought 8K (as seen on Linux) is a bit too much.

I then did a quick check to make sure I could actually retrieve the number from an external application, changed the number, and forgot to revert the change.

@benegee benegee Oct 8, 2026

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While we are at it, naming is hard. Do you have other suggestions for the macro name?


#if T8_ENABLE_VTK
#define t8_vtk_locidx_array_type_t vtkTypeInt32Array /**< VTK array type for local indices */
Expand All @@ -65,8 +66,8 @@ typedef enum {
*/
typedef struct
{
t8_vtk_data_type_t type; /**< Describes of which type the data array is */
char description[BUFSIZ]; /**< String that describes the data. */
t8_vtk_data_type_t type; /**< Describes of which type the data array is */
char description[T8_VTK_MAX_STRING_LENGTH]; /**< String that describes the data. */
double *data;
/**< An array of length n*num_local_elements doubles with
n = 1 if type = T8_VTK_SCALAR, n = 3 if type = T8_VTK_VECTOR */
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14 changes: 7 additions & 7 deletions src/t8_vtk/t8_vtk_write_ASCII.cxx
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Expand Up @@ -720,7 +720,7 @@ t8_forest_vtk_write_points (t8_forest_t forest, FILE *vtufile, const int write_g
int freturn;
int sreturn;
int idata;
char description[BUFSIZ];
char description[T8_VTK_MAX_STRING_LENGTH];

T8_ASSERT (t8_forest_is_committed (forest));
T8_ASSERT (vtufile != NULL);
Expand Down Expand Up @@ -748,23 +748,23 @@ t8_forest_vtk_write_points (t8_forest_t forest, FILE *vtufile, const int write_g
for (idata = 0; idata < num_data; idata++) {
if (data[idata].type == T8_VTK_SCALAR) {
/* Write the description string. */
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
t8_debugf ("Warning: Truncated vtk point data description to '%s'\n", description);
}
freturn = t8_forest_vtk_write_cell_data (forest, vtufile, description, T8_VTK_FLOAT_NAME, "", 8,
t8_forest_vtk_vertices_scalar_kernel, write_ghosts, data[idata].data);
}
else {
char component_string[BUFSIZ];
char component_string[T8_VTK_MAX_STRING_LENGTH];
T8_ASSERT (data[idata].type == T8_VTK_VECTOR);
snprintf (component_string, BUFSIZ, "NumberOfComponents=\"3\"");
snprintf (component_string, T8_VTK_MAX_STRING_LENGTH, "NumberOfComponents=\"3\"");
/* Write the description string. */
sreturn = snprintf (description, BUFSIZ, "%s_%s", data[idata].description, "points");
sreturn = snprintf (description, T8_VTK_MAX_STRING_LENGTH, "%s_%s", data[idata].description, "points");

if (sreturn >= BUFSIZ) {
if (sreturn >= T8_VTK_MAX_STRING_LENGTH) {
/* The output was truncated */
/* Note: gcc >= 7.1 prints a warning if we
* do not check the return value of snprintf. */
Expand Down
4 changes: 2 additions & 2 deletions test/t8_IO/t8_gtest_vtk_writer.cxx
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Expand Up @@ -175,10 +175,10 @@ struct vtk_writer_test: public testing::Test

// Fill the vtk_data descriptors
vtk_data[0].type = T8_VTK_SCALAR;
strncpy (vtk_data[0].description, "Testdata scalar i/10.", BUFSIZ);
strncpy (vtk_data[0].description, "Testdata scalar i/10.", T8_VTK_MAX_STRING_LENGTH);
vtk_data[0].data = scalar_data.data ();
vtk_data[1].type = T8_VTK_VECTOR;
strncpy (vtk_data[1].description, "Testdata vector (i/10.,-i/10.,42)", BUFSIZ);
strncpy (vtk_data[1].description, "Testdata vector (i/10.,-i/10.,42)", T8_VTK_MAX_STRING_LENGTH);
vtk_data[1].data = vector_data.data ();

writer = new vtk_writer<grid_t> (true, true, true, true, true, true, std::string ("test_vtk_writer"), num_vtk_data,
Expand Down
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