diff --git a/src/compute_chunk_atom.cpp b/src/compute_chunk_atom.cpp
index 92567101de..34bd855879 100644
--- a/src/compute_chunk_atom.cpp
+++ b/src/compute_chunk_atom.cpp
@@ -36,6 +36,7 @@
 #include "math_const.h"
 #include "memory.h"
 #include "error.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace MathConst;
@@ -581,21 +582,9 @@ void ComputeChunkAtom::init()
   // fixstore initializes all values to 0.0
 
   if ((idsflag == ONCE || lockcount) && !fixstore) {
-    int n = strlen(id) + strlen("_COMPUTE_STORE") + 1;
-    id_fix = new char[n];
-    strcpy(id_fix,id);
-    strcat(id_fix,"_COMPUTE_STORE");
-
-    char **newarg = new char*[6];
-    newarg[0] = id_fix;
-    newarg[1] = group->names[igroup];
-    newarg[2] = (char *) "STORE";
-    newarg[3] = (char *) "peratom";
-    newarg[4] = (char *) "1";
-    newarg[5] = (char *) "1";
-    modify->add_fix(6,newarg);
+    modify->add_fix(fmt::format("{}_COMPUTE_STORE {} STORE peratom 1 1",
+                                id,group->names[igroup]));
     fixstore = (FixStore *) modify->fix[modify->nfix-1];
-    delete [] newarg;
   }
 
   if ((idsflag != ONCE && !lockcount) && fixstore) {
diff --git a/src/compute_displace_atom.cpp b/src/compute_displace_atom.cpp
index 41db4db1d6..9a82924acb 100644
--- a/src/compute_displace_atom.cpp
+++ b/src/compute_displace_atom.cpp
@@ -24,6 +24,7 @@
 #include "variable.h"
 #include "memory.h"
 #include "error.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 
@@ -72,21 +73,9 @@ ComputeDisplaceAtom::ComputeDisplaceAtom(LAMMPS *lmp, int narg, char **arg) :
   // create a new fix STORE style
   // id = compute-ID + COMPUTE_STORE, fix group = compute group
 
-  int n = strlen(id) + strlen("_COMPUTE_STORE") + 1;
-  id_fix = new char[n];
-  strcpy(id_fix,id);
-  strcat(id_fix,"_COMPUTE_STORE");
-
-  char **newarg = new char*[6];
-  newarg[0] = id_fix;
-  newarg[1] = group->names[igroup];
-  newarg[2] = (char *) "STORE";
-  newarg[3] = (char *) "peratom";
-  newarg[4] = (char *) "1";
-  newarg[5] = (char *) "3";
-  modify->add_fix(6,newarg);
+  modify->add_fix(fmt::format("{}_COMPUTE_STORE {} STORE peratom 1 3",
+                              id,group->names[igroup]));
   fix = (FixStore *) modify->fix[modify->nfix-1];
-  delete [] newarg;
 
   // calculate xu,yu,zu for fix store array
   // skip if reset from restart file
diff --git a/src/modify.cpp b/src/modify.cpp
index f540116641..52a0ed50b8 100644
--- a/src/modify.cpp
+++ b/src/modify.cpp
@@ -941,6 +941,23 @@ void Modify::add_fix(int narg, char **arg, int trysuffix)
   fix[ifix]->post_constructor();
 }
 
+/* ----------------------------------------------------------------------
+   convenience function to allow adding a fix from a single string
+------------------------------------------------------------------------- */
+
+void Modify::add_fix(const std::string &fixcmd, int trysuffix)
+{
+  std::vector<std::string> args = utils::split_words(fixcmd);
+  char **newarg = new char*[args.size()];
+  int i=0;
+  for (const auto &arg : args) {
+    newarg[i++] = (char *)arg.c_str();
+  }
+  add_fix(args.size(),newarg,trysuffix);
+  delete[] newarg;
+}
+
+
 /* ----------------------------------------------------------------------
    replace replaceID fix with a new fix
    this is used by callers to preserve ordering of fixes
@@ -1228,6 +1245,23 @@ void Modify::add_compute(int narg, char **arg, int trysuffix)
   ncompute++;
 }
 
+/* ----------------------------------------------------------------------
+   convenience function to allow adding a compute from a single string
+------------------------------------------------------------------------- */
+
+void Modify::add_compute(const std::string &computecmd, int trysuffix)
+{
+  std::vector<std::string> args = utils::split_words(computecmd);
+  char **newarg = new char*[args.size()];
+  int i=0;
+  for (const auto &arg : args) {
+    newarg[i++] = (char *)arg.c_str();
+  }
+  add_compute(args.size(),newarg,trysuffix);
+  delete[] newarg;
+}
+
+
 /* ----------------------------------------------------------------------
    one instance per compute in style_compute.h
 ------------------------------------------------------------------------- */
diff --git a/src/modify.h b/src/modify.h
index 0b809d4d6a..a6cb5feab0 100644
--- a/src/modify.h
+++ b/src/modify.h
@@ -96,6 +96,7 @@ class Modify : protected Pointers {
   virtual int min_reset_ref();
 
   void add_fix(int, char **, int trysuffix=1);
+  void add_fix(const std::string &, int trysuffix=1);
   void replace_fix(const char *, int, char **, int trysuffix=1);
   void modify_fix(int, char **);
   void delete_fix(const char *);
@@ -108,6 +109,7 @@ class Modify : protected Pointers {
   int check_rigid_list_overlap(int *);
 
   void add_compute(int, char **, int trysuffix=1);
+  void add_compute(const std::string &, int trysuffix=1);
   void modify_compute(int, char **);
   void delete_compute(const char *);
   int find_compute(const char *);
diff --git a/src/output.cpp b/src/output.cpp
index ee3d5b3996..42d73f2c31 100644
--- a/src/output.cpp
+++ b/src/output.cpp
@@ -46,28 +46,13 @@ Output::Output(LAMMPS *lmp) : Pointers(lmp)
 {
   // create default computes for temp,pressure,pe
 
-  char **newarg = new char*[4];
-  newarg[0] = (char *) "thermo_temp";
-  newarg[1] = (char *) "all";
-  newarg[2] = (char *) "temp";
-  modify->add_compute(3,newarg);
-
-  newarg[0] = (char *) "thermo_press";
-  newarg[1] = (char *) "all";
-  newarg[2] = (char *) "pressure";
-  newarg[3] = (char *) "thermo_temp";
-  modify->add_compute(4,newarg);
-
-  newarg[0] = (char *) "thermo_pe";
-  newarg[1] = (char *) "all";
-  newarg[2] = (char *) "pe";
-  modify->add_compute(3,newarg);
-
-  delete [] newarg;
+  modify->add_compute("thermo_temp all temp");
+  modify->add_compute("thermo_press all pressure thermo_temp");
+  modify->add_compute("thermo_pe all pe");
 
   // create default Thermo class
 
-  newarg = new char*[1];
+  char **newarg = new char*[1];
   newarg[0] = (char *) "one";
   thermo = new Thermo(lmp,1,newarg);
   delete [] newarg;