[core] Check if string contains only ASCII symbols

function and test.

base/base_tests/string_utils_test.cpp

@@ -401,3 +401,14 @@ UNIT_TEST(UniString_LessAndEqualsAndNotEquals)
     }
   }
 }
+
+UNIT_TEST(IsUtf8Test)
+{
+  TEST(!strings::IsASCIIString("Нет"), ());
+  TEST(!strings::IsASCIIString("Классненькие места в Жодино.kml"), ());
+  TEST(!strings::IsASCIIString("在Zhodino陰涼處.kml"), ());
+  TEST(!strings::IsASCIIString("מקום קריר בZhodino.kml"), ());
+
+  TEST(strings::IsASCIIString("YES"), ());
+  TEST(strings::IsASCIIString("Nice places in Zhodino.kml"), ());
+}

base/string_utils.cpp

@@ -147,6 +147,14 @@ string ToUtf8(UniString const & s)
   return result;
 }
 
+bool IsASCIIString(string const & str)
+{
+  for (size_t i = 0; i < str.size(); ++i)
+    if (str[i] < 0 || str[i] > 127)
+      return false;
+  return true;
+}
+
 bool StartsWith(string const & s1, char const * s2)
 {
   return (s1.compare(0, strlen(s2), s2) == 0);

base/string_utils.hpp

@@ -43,6 +43,7 @@ bool EqualNoCase(string const & s1, string const & s2);
 
 UniString MakeUniString(string const & utf8s);
 string ToUtf8(UniString const & s);
+bool IsASCIIString(string const & str);
 
 inline string DebugPrint(UniString const & s)
 {