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correct documentation and simplify extracting vector length

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This commit is contained in:
Axel Kohlmeyer
2024-06-29 21:32:37 -04:00
parent 6ad0145709
commit f8a7fc787c
2 changed files with 23 additions and 14 deletions
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31
src/library.cpp
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@ -2420,7 +2420,7 @@ use to avoid a memory leak. Example:
.. code-block:: c
double *dptr = (double *) lammps_extract_variable(handle,name,NULL);
double *dptr = (double *) lammps_extract_variable(handle, name, NULL);
double value = *dptr;
lammps_free((void *)dptr);
@ -2431,16 +2431,25 @@ content will not be updated in case the variable is re-evaluated.
To avoid a memory leak, this pointer needs to be freed after use in
the calling program.
For *vector*\ -style variables, the returned pointer is to actual LAMMPS data.
The pointer should not be deallocated. Its length depends on the variable,
compute, or fix data used to construct the *vector*\ -style variable.
This length can be fetched by calling this function with *group* set to the
constant "LMP_SIZE_VECTOR", which returns a ``void *`` pointer that can be
dereferenced to an integer that is the length of the vector. This pointer
needs to be deallocated when finished with it to avoid memory leaks.
For *vector*\ -style variables, the returned pointer points to actual
LAMMPS data and thus it should **not** be deallocated. Its length
depends on the variable, compute, or fix data used to construct the
*vector*\ -style variable. This length can be fetched by calling this
function with *group* set to a non-NULL pointer (NULL returns the vector).
In that case it will return the vector length as an allocated int
pointer cast to a ``void *`` pointer. That pointer can be recast and
dereferenced to an integer yielding the length of the vector. This pointer
must be deallocated when finished with it to avoid memory leaks. Example:
.. code-block:: c
double *vectvals = (double *) lammps_extract_variable(handle, name, NULL);
int *intptr = (int *) lammps_extract_variable(handle, name, 1);
int vectlen = *intptr;
lammps_free((void *)intptr);
For other variable styles the returned pointer needs to be cast to
a char pointer. It should not be deallocated.
a char pointer and it should **not** be deallocated. Example:
.. code-block:: c
@ -2452,7 +2461,7 @@ a char pointer. It should not be deallocated.
LAMMPS cannot easily check if it is valid to access the data
referenced by the variables (e.g., computes, fixes, or thermodynamic
info), so it may fail with an error. The caller has to make certain
that the data are extracted only when it safe to evaluate the variable
that the data is extracted only when it safe to evaluate the variable
and thus an error or crash are avoided.
\endverbatim
@ -2487,7 +2496,7 @@ void *lammps_extract_variable(void *handle, const char *name, const char *group)
} else if (lmp->input->variable->vectorstyle(ivar)) {
double *values = nullptr;
int nvector = lmp->input->variable->compute_vector(ivar, &values);
if (group != nullptr && strcmp(group,"LMP_SIZE_VECTOR") == 0) {
if (group) {
int* nvecptr = (int *) malloc(sizeof(int));
*nvecptr = nvector;
return (void *) nvecptr;

6
src/library.h
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@ -175,9 +175,9 @@ void *lammps_extract_atom(void *handle, const char *name);
* Library functions to access data from computes, fixes, variables in LAMMPS
* ---------------------------------------------------------------------- */
void *lammps_extract_compute(void *handle, const char *, int, int);
void *lammps_extract_fix(void *handle, const char *, int, int, int, int);
void *lammps_extract_variable(void *handle, const char *, const char *);
void *lammps_extract_compute(void *handle, const char *id, int style, int type);
void *lammps_extract_fix(void *handle, const char *id, int style, int type, int nrow, int ncol);
void *lammps_extract_variable(void *handle, const char *name, const char *group);
int lammps_extract_variable_datatype(void *handle, const char *name);
int lammps_set_variable(void *handle, const char *name, const char *str);
int lammps_set_string_variable(void *handle, const char *name, const char *str);