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# DMLabelCompare
Compare two `DMLabel` objects
## Synopsis
```
#include "petscdmlabel.h"
#include "petscsection.h"
PetscErrorCode DMLabelCompare(MPI_Comm comm, DMLabel l0, DMLabel l1, PetscBool *equal, char **message)
```
Collective; No Fortran Support
## Input Parameters
- ***comm -*** Comm over which to compare labels
- ***l0 -*** First `DMLabel`
- ***l1 -*** Second `DMLabel`
Output Parameters
- ***equal -*** (Optional) Flag whether the two labels are equal
- ***message -*** (Optional) Message describing the difference
## Notes
The output flag equal is the same on all processes.
If it is passed as `NULL` and difference is found, an error is thrown on all processes.
Make sure to pass `NULL` on all processes.
The output message is set independently on each rank.
It is set to `NULL` if no difference was found on the current rank. It must be freed by user.
If message is passed as `NULL` and difference is found, the difference description is printed to stderr in synchronized manner.
Make sure to pass `NULL` on all processes.
For the comparison, we ignore the order of stratum values, and strata with no points.
The communicator needs to be specified because currently `DMLabel` can live on `PETSC_COMM_SELF` even if the underlying `DM` is parallel.
## See Also
`DMLabel`, `DM`, `DMCompareLabels()`, `DMLabelGetNumValues()`, `DMLabelGetDefaultValue()`, `DMLabelGetNonEmptyStratumValuesIS()`, `DMLabelGetStratumIS()`
## Level
intermediate
## Location
src/dm/label/dmlabel.c
## Examples
src/dm/label/tutorials/ex1.c
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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/dm/label/dmlabel.c)
[Index of all DMLabel routines](index.md)
[Table of Contents for all manual pages](/manualpages/index.md)
[Index of all manual pages](/manualpages/singleindex.md)