core: backport toLowerCase()/toUpperCase()

modules/core/include/opencv2/core/cvstd.hpp

@@ -1026,6 +1026,40 @@ static inline bool operator>= (const String& lhs, const String& rhs) { return lh
 static inline bool operator>= (const char*   lhs, const String& rhs) { return rhs.compare(lhs) <= 0; }
 static inline bool operator>= (const String& lhs, const char*   rhs) { return lhs.compare(rhs) >= 0; }
 
+
+#ifndef OPENCV_DISABLE_STRING_LOWER_UPPER_CONVERSIONS
+
+//! @cond IGNORED
+namespace details {
+// std::tolower is int->int
+static inline char char_tolower(char ch)
+{
+    return (char)std::tolower((int)ch);
+}
+// std::toupper is int->int
+static inline char char_toupper(char ch)
+{
+    return (char)std::toupper((int)ch);
+}
+} // namespace details
+//! @endcond
+
+static inline std::string toLowerCase(const std::string& str)
+{
+    std::string result(str);
+    std::transform(result.begin(), result.end(), result.begin(), details::char_tolower);
+    return result;
+}
+
+static inline std::string toUpperCase(const std::string& str)
+{
+    std::string result(str);
+    std::transform(result.begin(), result.end(), result.begin(), details::char_toupper);
+    return result;
+}
+
+#endif // OPENCV_DISABLE_STRING_LOWER_UPPER_CONVERSIONS
+
 //! @} relates cv::String
 
 } // cv