:orphan:
# PetscPoisonMemoryRegion
Poison a region in memory, making it undereferencable 
## Synopsis
```
static inline PetscErrorCode PetscPoisonMemoryRegion(const void *ptr, size_t size)
```
Not Available From Fortran


## Input Parameters

- ***ptr  -*** The pointer to the start of the region
- ***size -*** The size (in bytes) of the region to poison



## Notes
`ptr` must not be `NULL`. It is OK to poison the same memory region repeatedly (it is a
no-op).

Any attempt to dereference the region after this routine returns results in an error being
raised. The memory region may be un-poisoned using `PetscUnpoisonMemoryRegion()`, making it
safe to dereference again.


## Example Usage
```none
  PetscInt *array;

  PetscMalloc1(15, &array);
  // OK, memory is normal
  array[0] = 10;
  array[1] = 15;

  PetscPoisonMemoryRegion(array, 15 * sizeof(*array));
  // ERROR this region is poisoned!
  array[0] = 10;
  // ERROR reading is not allowed either!
  PetscInt v = array[15];

  // OK can re-poison the region
  PetscPoisonMemoryRegion(array, 15 * sizeof(*array));
  // OK can re-poison any subregion too
  PetscPoisonMemoryRegion(array + 5, 1 * sizeof(*array));

  PetscUnpoisonMemoryRegion(array, 1 * sizeof(*array));
  // OK the first entry has been unpoisoned
  array[0] = 10;
  // ERROR the rest of the region is still poisoned!
  array[1] = 12345;

  PetscUnpoisonMemoryRegion(array + 10, sizeof(*array));
  // OK this region is unpoisoned (even though surrounding memory is still poisoned!)
  array[10] = 0;

  PetscInt stack_array[10];

  // OK can poison stack memory as well
  PetscPoisonMemoryRegion(stack_array, 10 * sizeof(*stack_array));
  // ERROR stack array is poisoned!
  stack_array[0] = 10;
```





## See Also
 `PetscUnpoisonMemoryRegion()`, `PetscIsRegionPoisoned()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petsc/private/mempoison.h.html#PetscPoisonMemoryRegion">include/petsc/private/mempoison.h</A>


---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/include/petsc/private/mempoison.h)


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