Changed the code in the read_F_table function to conform to the "expected behavior" description in #1572. Adopted a best-of-both-worlds approach, though, and processed the whole input file all the way through, emitting a message for each problem found, before issuing a final error message to stop processing. Updated doc to clarify requirement for uniform spacing of pressure correction points.

doc/src/fix_bocs.txt

@@ -47,13 +47,13 @@ or {cubic_spline}.
 
 With either spline method, the only argument that needs to follow it
 is the name of a file that contains the desired pressure correction
-as a function of volume. The file should be formatted so each line has:
+as a function of volume. The file must be formatted so each line has:
 
 Volume_i, PressureCorrection_i :pre
 
 Note both the COMMA and the SPACE separating the volume's
 value and its corresponding pressure correction. The volumes in the file
-should be uniformly spaced. Both the volumes and the pressure corrections
+must be uniformly spaced. Both the volumes and the pressure corrections
 should be provided in the proper units, e.g. if you are using {units real},
 the volumes should all be in cubic angstroms, and the pressure corrections
 should all be in atmospheres. Furthermore, the table should start/end at a

src/USER-BOCS/fix_bocs.cpp

@@ -59,6 +59,9 @@ enum{NOBIAS,BIAS};
 enum{NONE,XYZ,XY,YZ,XZ};
 enum{ISO,ANISO,TRICLINIC};
 
+// NB: Keep error and warning messages less than 255 chars long.
+const int MAX_MESSAGE_LENGTH = 256;
+
 /* ----------------------------------------------------------------------
    NVT,NPH,NPT integrators for improved Nose-Hoover equations of motion
  ---------------------------------------------------------------------- */
@@ -630,24 +633,32 @@ int FixBocs::read_F_table( char *filename, int p_basis_type )
   double **data = (double **) calloc(N_columns,sizeof(double *));
   char * line = (char *) calloc(200,sizeof(char));
 
+  bool badInput = false;
+  char badDataMsg[MAX_MESSAGE_LENGTH];
   fpi = fopen(filename,"r");
   if (fpi)
   {
     while (fgets(line,199,fpi)) { ++n_entries; }
-    fclose(fpi);
+
     for (i = 0; i < N_columns; ++i)
     {
       data[i] = (double *) calloc(n_entries,sizeof(double));
     }
-  } else {
-    char errmsg[128];
-    snprintf(errmsg,128,"Unable to open file: %s\n",filename);
-    error->all(FLERR,errmsg);
-  }
 
-  n_entries = 0;
-  fpi = fopen(filename,"r");
-  if (fpi) {
+    // Don't need to re-open the file to make a second pass through it
+    // simply rewind to beginning
+    rewind(fpi);
+
+    double stdVolumeInterval = 0.0;
+    double currVolumeInterval = 0.0;
+    // When comparing doubles/floats, we need an Epsilon.
+    // The literature indicates getting this value right in the
+    // general case can be pretty complicated. I don't think it
+    // needs to be complicated here, though. At least based on the
+    // sample data I've seen where the volume values are fairly
+    // large.
+    const double volumeIntervalTolerance = 0.001;
+    n_entries = 0;
     while( fgets(line,199,fpi)) {
       ++n_entries;
       test_sscanf = sscanf(line," %f , %f ",&f1, &f2);
@@ -655,19 +666,47 @@ int FixBocs::read_F_table( char *filename, int p_basis_type )
       {
         data[0][n_entries-1] = (double) f1;
         data[1][n_entries-1] = (double) f2;
+        if (n_entries == 2) {
+          stdVolumeInterval = data[0][n_entries-1] - data[0][n_entries-2];
+        }
+        else if (n_entries > 2) {
+          currVolumeInterval = data[0][n_entries-1] - data[0][n_entries-2];
+          if (fabs(currVolumeInterval - stdVolumeInterval) > volumeIntervalTolerance) {
+            snprintf(badDataMsg,MAX_MESSAGE_LENGTH,
+                     "BAD VOLUME INTERVAL: spline analysis requires uniform"
+                     " volume distribution, found inconsistent volume"
+                     " differential, line %d of file %s\n\tline: %s",
+                     n_entries,filename,line);
+            error->message(FLERR,badDataMsg);
+            badInput = true;
+          }
+        }
+        // no else -- first entry is simply ignored
       }
       else
       {
-        fprintf(stderr,"WARNING: did not find 2 comma separated values in "
-                 "line %d of file %s\n\tline: %s",n_entries,filename,line);
+        snprintf(badDataMsg,MAX_MESSAGE_LENGTH,
+                 "BAD INPUT FORMAT: did not find 2 comma separated numeric"
+                 " values in line %d of file %s\n\tline: %s",
+                 n_entries,filename,line);
+        error->message(FLERR,badDataMsg);
+        badInput = true;
       }
     }
-  } else {
-    char errmsg[128];
-    snprintf(errmsg,128,"Unable to open file: %s\n",filename);
+    fclose(fpi);
+  }
+  else {
+    char errmsg[MAX_MESSAGE_LENGTH];
+    snprintf(errmsg,MAX_MESSAGE_LENGTH,"Unable to open file: %s\n",filename);
+    error->all(FLERR,errmsg);
+  }
+
+  if (badInput) {
+    char errmsg[MAX_MESSAGE_LENGTH];
+    snprintf(errmsg,MAX_MESSAGE_LENGTH,
+             "Bad volume / pressure-correction data: %s\nSee details above",filename);
     error->all(FLERR,errmsg);
   }
-  fclose(fpi);
 
   if (p_basis_type == 1)
   {
@@ -691,9 +730,10 @@ int FixBocs::read_F_table( char *filename, int p_basis_type )
   }
   else
   {
-    char * errmsg = (char *) calloc(70,sizeof(char));
-    sprintf(errmsg,"ERROR: invalid p_basis_type value "
-                                    "of %d in read_F_table",p_basis_type);
+    char errmsg[MAX_MESSAGE_LENGTH];
+    snprintf(errmsg, MAX_MESSAGE_LENGTH,
+             "ERROR: invalid p_basis_type value of %d in read_F_table",
+             p_basis_type);
     error->all(FLERR,errmsg);
   }
   // cleanup