refactor variable info in Info class, make info accessible from library interface

doc/src/Library_objects.rst

@@ -9,6 +9,7 @@ fixes, or variables in LAMMPS using the following functions:
 - :cpp:func:`lammps_extract_variable_datatype`
 - :cpp:func:`lammps_extract_variable`
 - :cpp:func:`lammps_set_variable`
+- :cpp:func:`lammps_variable_info`
 
 -----------------------
 
@@ -37,6 +38,11 @@ fixes, or variables in LAMMPS using the following functions:
 
 -----------------------
 
+.. doxygenfunction:: lammps_variable_info
+   :project: progguide
+
+-----------------------
+
 .. doxygenenum:: _LMP_DATATYPE_CONST
 
 .. doxygenenum:: _LMP_STYLE_CONST

examples/COUPLE/plugin/liblammpsplugin.c

@@ -110,6 +110,7 @@ liblammpsplugin_t *liblammpsplugin_load(const char *lib)
   ADDSYM(extract_variable);
   ADDSYM(extract_variable_datatype);
   ADDSYM(set_variable);
+  ADDSYM(variable_info);
 
   ADDSYM(gather_atoms);
   ADDSYM(gather_atoms_concat);

examples/COUPLE/plugin/liblammpsplugin.h

@@ -155,6 +155,7 @@ struct _liblammpsplugin {
   void *(*extract_variable)(void *, const char *, char *);
   int (*extract_variable_datatype)(void *, const char *);
   int (*set_variable)(void *, char *, char *);
+  int (*variable_info)(void *, int, char *, int);
 
   void (*gather_atoms)(void *, const char *, int, int, void *);
   void (*gather_atoms_concat)(void *, const char *, int, int, void *);

src/info.cpp

@@ -601,23 +601,10 @@ void Info::command(int narg, char **arg)
 
   if (flags & VARIABLES) {
     int nvar = input->variable->nvar;
-    int *style = input->variable->style;
-    char **names = input->variable->names;
-    char ***data = input->variable->data;
     fputs("\nVariable information:\n",out);
     for (int i=0; i < nvar; ++i) {
-      int ndata = 1;
-      fmt::print(out,"Variable[{:3d}]: {:16}  style = {:16}  def =",
-                 i,std::string(names[i])+',',std::string(varstyles[style[i]])+',');
-      if (style[i] == Variable::INTERNAL) {
-        fmt::print(out,"{:.8}\n",input->variable->dvalue[i]);
-        continue;
-      }
-      if ((style[i] != Variable::LOOP) && (style[i] != Variable::ULOOP))
-        ndata = input->variable->num[i];
-      for (int j=0; j < ndata; ++j)
-        if (data[i][j]) fmt::print(out," {}",data[i][j]);
-      fputs("\n",out);
+      auto vinfo = get_variable_info(i);
+      fmt::print(out, get_variable_info(i));
     }
   }
 
@@ -1316,3 +1303,29 @@ char **Info::get_variable_names(int &num) {
   num = input->variable->nvar;
   return input->variable->names;
 }
+
+/* ---------------------------------------------------------------------- */
+
+std::string Info::get_variable_info(int num) {
+  int *style = input->variable->style;
+  char **names = input->variable->names;
+  char ***data = input->variable->data;
+  std::string text;
+  int ndata = 1;
+  text = fmt::format("Variable[{:3d}]: {:16}  style = {:16}  def =", num,
+                     std::string(names[num]) + ',', std::string(varstyles[style[num]]) + ',');
+  if (style[num] == Variable::INTERNAL) {
+    text += fmt::format("{:.8}\n",input->variable->dvalue[num]);
+    return text;
+  }
+
+  if ((style[num] != Variable::LOOP) && (style[num] != Variable::ULOOP))
+    ndata = input->variable->num[num];
+  else
+    input->variable->retrieve(names[num]);
+
+  for (int j=0; j < ndata; ++j)
+    if (data[num][j]) text += fmt::format(" {}",data[num][j]);
+  text += "\n";
+  return text;
+}

src/info.h

@@ -53,6 +53,7 @@ class Info : public Command {
 
   void get_memory_info(double *);
   char **get_variable_names(int &num);
+  std::string get_variable_info(int num);
 
  private:
   void available_styles(FILE *out, int flags);

src/library.cpp

@@ -2460,6 +2460,42 @@ int lammps_set_variable(void *handle, char *name, char *str)
   return err;
 }
 
+
+/* ---------------------------------------------------------------------- */
+
+/** Retrieve informational string for a variable.
+ *
+ * .. versionadded:: TBD
+ *
+ * This function copies a string with human readable information about
+ * a defined variable: name, style, current value(s) into the provided
+ * C-style string buffer.  That is the same info as produced by the
+ * :doc:`info variables <info>` command. The length of the buffer must
+ * be provided as *buf_size* argument.  If the info exceeds the length
+ * of the buffer, it will be truncated accordingly.  If the index is
+ * out of range, the function returns 0 and *buffer* is set to an empty
+ * string, otherwise 1.
+ *
+ * \param handle   pointer to a previously created LAMMPS instance cast to ``void *``.
+ * \param idx      index of the variable (0 <= idx < nvar)
+ * \param buffer   string buffer to copy the info to
+ * \param buf_size size of the provided string buffer
+ * \return 1 if successful, otherwise 0  */
+
+int lammps_variable_info(void *handle, int idx, char *buffer, int buf_size) {
+  auto lmp = (LAMMPS *) handle;
+  Info info(lmp);
+  auto varinfo = info.get_variable_info(idx);
+
+  if ((idx >= 0) && (idx < lmp->input->variable->nvar)) {
+    strncpy(buffer, varinfo.c_str(), buf_size);
+    return 1;
+  }
+
+  buffer[0] = '\0';
+  return 0;
+}
+
 // ----------------------------------------------------------------------
 // Library functions for scatter/gather operations of data
 // ----------------------------------------------------------------------

src/library.h

@@ -177,7 +177,8 @@ 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 *);
 int lammps_extract_variable_datatype(void *handle, const char *name);
-int lammps_set_variable(void *, char *, char *);
+int lammps_set_variable(void *handle, char *name, char *str);
+int lammps_variable_info(void *handle, int idx, char *buf, int bufsize);
 
 /* ----------------------------------------------------------------------
  * Library functions for scatter/gather operations of data
@@ -198,11 +199,11 @@ void lammps_gather_impropers(void *handle, void *data);
 
 void lammps_gather(void *handle, const char *name, int type, int count, void *data);
 void lammps_gather_concat(void *handle, const char *name, int type, int count, void *data);
-void lammps_gather_subset(void *handle, const char *name, int type, int count, int ndata,
-                          int *ids, void *data);
+void lammps_gather_subset(void *handle, const char *name, int type, int count, int ndata, int *ids,
+                          void *data);
 void lammps_scatter(void *handle, const char *name, int type, int count, void *data);
-void lammps_scatter_subset(void *handle, const char *name, int type, int count, int ndata,
-                           int *ids, void *data);
+void lammps_scatter_subset(void *handle, const char *name, int type, int count, int ndata, int *ids,
+                           void *data);
 
 #if !defined(LAMMPS_BIGBIG)
 int lammps_create_atoms(void *handle, int n, const int *id, const int *type, const double *x,

tools/lammps-gui/lammpswrapper.cpp

@@ -97,6 +97,19 @@ int LammpsWrapper::id_name(const char *keyword, int idx, char *buf, int len)
     return val;
 }
 
+int LammpsWrapper::variable_info(int idx, char *buf, int len)
+{
+    int val = 0;
+    if (lammps_handle) {
+#if defined(LAMMPS_GUI_USE_PLUGIN)
+        val = ((liblammpsplugin_t *)plugin_handle)->variable_info(lammps_handle, idx, buf, len);
+#else
+        val = lammps_variable_info(lammps_handle, idx, buf, len);
+#endif
+    }
+    return val;
+}
+
 double LammpsWrapper::get_thermo(const char *keyword)
 {
     double val = 0.0;

tools/lammps-gui/lammpswrapper.h

@@ -35,6 +35,7 @@ public:
 
     int id_count(const char *idtype);
     int id_name(const char *idtype, int idx, char *buf, int buflen);
+    int variable_info(int idx, char *buf, int buflen);
 
     double get_thermo(const char *keyword);
     void *last_thermo(const char *keyword, int idx);