Implement some cppcheck messages. (#155)

* Use standard C++ idioms

Static analyser cppcheck found a few places where
strings were passed by value. 

Standard C++ uses const references.

* Update StringUtils.h: end_with

I changed the wrong parameter.

* Update StringUtils.cpp

cppcheck recommended these changes.

src/StringUtils.cpp

@@ -112,7 +112,7 @@ StringUtils::find_any_char(const string &s, size_t pos, const string& to_match)
 }
 
 void
-StringUtils::split_string(const string str, vector<string> &v, const char sep_char)
+StringUtils::split_string(const string &str, vector<string> &v, const char sep_char)
 {
 	size_t pos = 0;
 	size_t start_pos = 0;
@@ -131,7 +131,7 @@ StringUtils::split_string(const string str, vector<string> &v, const char sep_ch
 }
 
 void
-StringUtils::split_string(const string str, vector<string> &v, string sep_chars)
+StringUtils::split_string(const string &str, vector<string> &v, string sep_chars)
 {
 	size_t pos = 0;
 	size_t start_pos = 0;
@@ -150,7 +150,7 @@ StringUtils::split_string(const string str, vector<string> &v, string sep_chars)
 }
 
 void
-StringUtils::split_int_string(const string str, vector<int> &values, string sep_chars)
+StringUtils::split_int_string(const string &str, vector<int> &values, string sep_chars)
 {
 	size_t pos = 0;
 	size_t start_pos = 0;
@@ -264,7 +264,7 @@ StringUtils::breakup_assigns(const string& assigns, vector<string>& vars, vector
 }
 
 bool
-StringUtils::end_with(string s, string tail)
+StringUtils::end_with(string s, const string &tail)
 {
 	if (tail.length() < s.length()) {
 		s = s.substr(s.length() - tail.length());

src/StringUtils.h

@@ -41,7 +41,7 @@ class StringUtils {
 
 	static bool is_space(const char c);
 
-	static bool end_with(string s, string tail);
+	static bool end_with(string s, const string &tail);
 
 	static void ignore_spaces(const std::string &str, size_t &pos);
 
@@ -61,11 +61,11 @@ class StringUtils {
 
 	static size_t find_any_char(const string &s, size_t pos, const string& to_match);
 
-	static void split_string(const string str, vector<string> &v, const char sep_char);
+	static void split_string(const string &str, vector<string> &v, const char sep_char);
 
-	static void split_string(const string str, vector<string> &v, string sep_chars);
+	static void split_string(const string &str, vector<string> &v, string sep_chars);
 
-	static void split_int_string(const string str, vector<int> &values, string sep_chars);
+	static void split_int_string(const string &str, vector<int> &values, string sep_chars);
 
 	static void chop(string& str);