use regex for matching cv types (#202)

* use regex for matching cv types

Signed-off-by: Kenji Brameld <kenjibrameld@gmail.com>

* Update sensor_msgs/include/sensor_msgs/image_encodings.hpp

Co-authored-by: Geoffrey Biggs <gbiggs@killbots.net>
Signed-off-by: Kenji Brameld <kenjibrameld@gmail.com>

* Update sensor_msgs/include/sensor_msgs/image_encodings.hpp

Co-authored-by: Geoffrey Biggs <gbiggs@killbots.net>
Signed-off-by: Kenji Brameld <kenjibrameld@gmail.com>

Signed-off-by: Kenji Brameld <kenjibrameld@gmail.com>
Co-authored-by: Geoffrey Biggs <gbiggs@killbots.net>

sensor_msgs/include/sensor_msgs/image_encodings.hpp

@@ -33,6 +33,7 @@
 #define SENSOR_MSGS__IMAGE_ENCODINGS_HPP_
 
 #include <cstdlib>
+#include <regex>
 #include <stdexcept>
 #include <string>
 
@@ -109,6 +110,8 @@ const char ABSTRACT_ENCODING_PREFIXES[][5] = {
   "8UC", "8SC", "16UC", "16SC", "32SC", "32FC", "64FC"
 };
 
+const std::regex cv_type_regex("(8|16|32|64)(U|S|F)C([0-9]*)");
+
 // Utility functions for inspecting an encoding string
 static inline bool isColor(const std::string & encoding)
 {
@@ -172,24 +175,10 @@ static inline int numChannels(const std::string & encoding)
   }
 
   // Now all the generic content encodings
-  // TODO(clalancette): Rewrite with regex when ROS supports C++11
-  for (size_t i = 0; i < sizeof(ABSTRACT_ENCODING_PREFIXES) / sizeof(*ABSTRACT_ENCODING_PREFIXES);
-    i++)
-  {
-    std::string prefix = ABSTRACT_ENCODING_PREFIXES[i];
-    if (encoding.substr(0, prefix.size()) != prefix) {
-      continue;
-    }
-    if (encoding.size() == prefix.size()) {
-      return 1;  // ex. 8UC -> 1
-    }
-    int n_channel = atoi(
-      encoding.substr(
-        prefix.size(), encoding.size() - prefix.size()
-      ).c_str());  // ex. 8UC5 -> 5
-    if (n_channel != 0) {
-      return n_channel;  // valid encoding string
-    }
+  std::cmatch m;
+  // ex. 8UC -> 1, 8UC5 -> 5
+  if (std::regex_match(encoding.c_str(), m, cv_type_regex)) {
+    return (m[3] == "") ? 1 : std::atoi(m[3].str().c_str());
   }
 
   if (encoding == YUV422 ||
@@ -236,24 +225,10 @@ static inline int bitDepth(const std::string & encoding)
   }
 
   // Now all the generic content encodings
-  // TODO(clalancette): Rewrite with regex when ROS supports C++11
-  for (size_t i = 0; i < sizeof(ABSTRACT_ENCODING_PREFIXES) / sizeof(*ABSTRACT_ENCODING_PREFIXES);
-    i++)
-  {
-    std::string prefix = ABSTRACT_ENCODING_PREFIXES[i];
-    if (encoding.substr(0, prefix.size()) != prefix) {
-      continue;
-    }
-    if (encoding.size() == prefix.size()) {
-      return atoi(prefix.c_str());  // ex. 8UC -> 8
-    }
-    int n_channel = atoi(
-      encoding.substr(
-        prefix.size(), encoding.size() - prefix.size()
-      ).c_str());  // ex. 8UC10 -> 10
-    if (n_channel != 0) {
-      return atoi(prefix.c_str());  // valid encoding string
-    }
+  std::cmatch m;
+  // ex. 8UC -> 8, 8UC10 -> 10
+  if (std::regex_match(encoding.c_str(), m, cv_type_regex)) {
+    return std::atoi(m[0].str().c_str());
   }
 
   if (encoding == YUV422 ||