compare_versions: limit how many parts are checked.

This can be used to only check the first one or two parts of a version,
to ensure only the major, or major+minor parts match.

simgear/misc/strutils.cxx

@@ -372,12 +372,16 @@ namespace simgear {
         return result;
     }
 
-    int compare_versions(const string& v1, const string& v2)
+    int compare_versions(const string& v1, const string& v2, int maxComponents)
     {
         vector<string> v1parts(split(v1, "."));
         vector<string> v2parts(split(v2, "."));
 
         int lastPart = std::min(v1parts.size(), v2parts.size());
+        if (maxComponents > 0) {
+            lastPart = std::min(lastPart, maxComponents);
+        }
+
         for (int part=0; part < lastPart; ++part) {
             int part1 = to_int(v1parts[part]);
             int part2 = to_int(v2parts[part]);

simgear/misc/strutils.hxx

@@ -174,8 +174,10 @@ namespace simgear {
      * any number of terms are supported.
      * @return 0 if versions match, -ve number if v1 is lower, +ve if v1
      * is greater
+     * @param maxComponents is the maximum number of components to look at.
+     * This can be used to ignore (say) the patch level by setting it to 2
      */
-    int compare_versions(const std::string& v1, const std::string& v2);
+    int compare_versions(const std::string& v1, const std::string& v2, int maxComponents = 0);
 
     /**
      * Convert a string to upper case.

simgear/misc/strutils_test.cxx

@@ -155,6 +155,11 @@ void test_compare_versions()
 
   // Since we compare numerically, leading zeros shouldn't matter
   SG_CHECK_EQUAL(strutils::compare_versions("0.06.7", "0.6.07"), 0);
+
+
+  SG_CHECK_EQUAL(strutils::compare_versions("10.6.7", "10.6.8", 2), 0);
+  SG_CHECK_GT(strutils::compare_versions("10.7.7", "10.6.8", 2), 0);
+  SG_CHECK_EQUAL(strutils::compare_versions("10.8.7", "10.6.8", 1), 0);
 }
 
 void test_md5_hex()