add check that allows only %f and %g conversions in variable format strings

src/variable.cpp

@@ -38,6 +38,7 @@
 #include "memory.h"
 #include "info.h"
 #include "error.h"
+#include "utils.h"
 
 using namespace LAMMPS_NS;
 using namespace MathConst;
@@ -383,6 +384,8 @@ void Variable::set(int narg, char **arg)
     num[nvar] = 3;
     which[nvar] = 0;
     pad[nvar] = 0;
+    if (!utils::strmatch(arg[2],"%[0-9 ]*\\.[0-9]+[fg]"))
+      error->all(FLERR,"Incorrect conversion in format string");
     data[nvar] = new char*[num[nvar]];
     copy(2,&arg[2],data[nvar]);
     data[nvar][2] = new char[VALUELENGTH];