r.volume: Work with any mask name

Avoid hardcoded MASK by using the Rast_mask_status function. The rest of the logic stays the same so mask
is read just as the plain raster map is read.

Documentation is updated to use 'raster mask' instead of 'MASK'.

raster/r.volume/main.c

@@ -12,10 +12,10 @@
  *                 <landa.martin gmail.com>
  * PURPOSE:      r.volume is a program to compute the total, and average of
  *               cell values within regions of a map defined by clumps or
- *               patches on a second map (or MASK). It also computes the
- *               "volume" by multiplying the total within a clump by the area
- *               of each cell. It also outputs the "centroid" location of each
- *               clump. Output is to standard out.
+ *               patches on a second map (or by raster mask). It also computes
+ *               the "volume" by multiplying the total within a clump by the
+ *               area of each cell. It also outputs the "centroid" location of
+ *               each clump. Output is to standard out.
  *
  * COPYRIGHT:    (C) 1999-2006, 2013 by the GRASS Development Team
  *
@@ -43,7 +43,8 @@ int main(int argc, char *argv[])
     CELL i, max;
 
     int row, col, rows, cols;
-    int out_mode, use_MASK;
+    int out_mode;
+    bool use_mask;
     unsigned long *n, *e;
     long int *count;
     int fd_data, fd_clump;
@@ -92,7 +93,8 @@ int main(int argc, char *argv[])
     opt.clump->required = NO;
     opt.clump->label = _("Name of input clump raster map");
     opt.clump->description = _("Preferably the output of r.clump. "
-                               "If no clump map is given than MASK is used.");
+                               "If no clump map is given, "
+                               "raster mask is used instead.");
 
     opt.centroids = G_define_standard_option(G_OPT_V_OUTPUT);
     opt.centroids->key = "centroids";
@@ -134,24 +136,28 @@ int main(int argc, char *argv[])
     out_mode = (!flag.report->answer);
 
     /*
-     * see if MASK or a separate "clumpmap" raster map is to be used
+     * see if raster mask or a separate "clumpmap" raster map is to be used
      * -- it must(!) be one of those two choices.
      */
-    use_MASK = 0;
+    use_mask = false;
+    char mask_name[GNAME_MAX];
+    char mask_mapset[GMAPSET_MAX];
     if (!clumpmap) {
-        clumpmap = "MASK";
-        use_MASK = 1;
-        if (!G_find_raster2(clumpmap, G_mapset()))
-            G_fatal_error(_("No MASK found. If no clump map is given than the "
-                            "MASK is required. "
-                            "You need to define a clump raster map or create a "
-                            "MASK by r.mask command."));
-        G_important_message(_("No clump map given, using MASK"));
+        bool present =
+            Rast_mask_status(mask_name, mask_mapset, NULL, NULL, NULL);
+        if (!present)
+            G_fatal_error(_("No clump map <%s> given and no raster mask found. "
+                            "You need to define a clump raster map or create "
+                            "a raster mask using r.mask."),
+                          opt.clump->key);
+        clumpmap = mask_name;
+        use_mask = true;
+        G_important_message(_("No clump map given, using raster mask"));
     }
 
     /* open input and clump raster maps */
     fd_data = Rast_open_old(datamap, "");
-    fd_clump = Rast_open_old(clumpmap, use_MASK ? G_mapset() : "");
+    fd_clump = Rast_open_old(clumpmap, use_mask ? mask_mapset : "");
 
     /* initialize vector map (for centroids) if needed */
     if (centroidsmap) {
@@ -175,7 +181,7 @@ int main(int argc, char *argv[])
     }
 
     /* initialize data accumulation arrays */
-    max = Rast_get_max_c_cat(clumpmap, use_MASK ? G_mapset() : "");
+    max = Rast_get_max_c_cat(clumpmap, use_mask ? mask_mapset : "");
 
     sum = (double *)G_malloc((max + 1) * sizeof(double));
     count = (long int *)G_malloc((max + 1) * sizeof(long int));

raster/r.volume/r.volume.html

@@ -8,7 +8,7 @@ <h2>DESCRIPTION</h2>
 from a <b>input</b> raster map sorted by category on a <b>clump</b>
 raster map, and optionally generates a vector points map of the
 centroids for each clump.  If a clump map is not specified, the
-current MASK is used. The MASK can be defined
+current raster mask is used. The raster mask can be defined
 by <em><a href="r.mask.html">r.mask</a></em>. The sum is multiplied by
 the area of a cell to give the volume occupied by that cell. See below
 for an example of the output table.
@@ -24,12 +24,12 @@ <h2>DESCRIPTION</h2>
 <h2>NOTES</h2>
 
 <p>
-If a clump map is not given and a MASK not set, the program exits with
-an error message.
+If a clump map is not given and a raster mask is not set, the program exits
+with an error message.
 
 <p>
 <em>r.volume</em> works in the current region and respects the current
-MASK.
+raster mask.
 
 <h3>CENTROIDS</h3>