Common: Simplify uppercase/lowercase string functions.

Also changed it to not modify the given string, but rather return a copy of it.

src/common/string_util.cpp

@@ -3,6 +3,7 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
+#include <cctype>
 #include <cstdlib>
 #include <cstdio>
 
@@ -18,19 +19,15 @@
 #endif
 
 /// Make a string lowercase
-void LowerStr(char* str) {
-    for (int i = 0; str[i]; i++) {
-        str[i] = tolower(str[ i ]);
-    }
+std::string ToLowerCaseString(std::string input) {
+    std::transform(input.begin(), input.end(), input.begin(), ::tolower);
+    return input;
 }
 
 /// Make a string uppercase
-void UpperStr(char* str) {
-    for (int i=0; i < strlen(str); i++) {
-        if(str[i] >= 'a' && str[i] <= 'z') {
-            str[i] &= 0xDF;
-        }
-    }
+std::string ToUpperCaseString(std::string input) {
+    std::transform(input.begin(), input.end(), input.begin(), ::toupper);
+    return input;
 }
 
 // faster than sscanf

src/common/string_util.h

@@ -13,10 +13,10 @@
 #include "common/common.h"
 
 /// Make a string lowercase
-void LowerStr(char* str);
+std::string ToLowerCaseString(std::string input);
 
 /// Make a string uppercase
-void UpperStr(char* str);
+std::string ToUpperCaseString(std::string input);
 
 std::string StringFromFormat(const char* format, ...);
 // Cheap!