From 8b1dedf04a3c16a6d21673734c64fb1ce9e90c79 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Fri, 16 Jul 2021 17:21:57 -0400
Subject: [PATCH] add extract method to fix external

---
 src/fix_external.cpp | 15 ++++++++++++++-
 src/fix_external.h   |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/fix_external.cpp b/src/fix_external.cpp
index 8bede4ee19..4bc1e7eebc 100644
--- a/src/fix_external.cpp
+++ b/src/fix_external.cpp
@@ -238,7 +238,7 @@ void FixExternal::set_virial_peratom(double **caller_virial)
 
 void FixExternal::set_vector_length(int n)
 {
-  delete [] caller_vector;
+  delete[] caller_vector;
 
   vector_flag = 1;
   size_vector = n;
@@ -342,3 +342,16 @@ void FixExternal::set_callback(FnPtr caller_callback, void *caller_ptr)
   callback = caller_callback;
   ptr_caller = caller_ptr;
 }
+
+/* ----------------------------------------------------------------------
+   get access to internal data structures
+------------------------------------------------------------------------- */
+
+void *FixExternal::extract(const char *str, int &dim)
+{
+  if (strcmp(str, "fexternal") == 0) {
+    dim = 2;
+    return (void *) fexternal;
+  }
+  return nullptr;
+}
diff --git a/src/fix_external.h b/src/fix_external.h
index 0ace978f99..f0f46cd4c5 100644
--- a/src/fix_external.h
+++ b/src/fix_external.h
@@ -57,6 +57,8 @@ class FixExternal : public Fix {
   typedef void (*FnPtr)(void *, bigint, int, tagint *, double **, double **);
   void set_callback(FnPtr, void *);
 
+  void *extract(const char *, int &);
+
  private:
   int mode, ncall, napply, eflag_caller;
   FnPtr callback;