[Bug #18955] Check length of argument for `%c` in proper encoding

2 files changed, 5 insertions, 2 deletions

diff --git a/sprintf.c b/sprintf.c
index b16ab3f581..5f7227e619 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -441,10 +441,11 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 
                 tmp = rb_check_string_type(val);
                 if (!NIL_P(tmp)) {
-                    if (rb_enc_strlen(RSTRING_PTR(tmp),RSTRING_END(tmp),enc) != 1) {
+                    rb_encoding *valenc = rb_enc_get(tmp);
+                    if (rb_enc_strlen(RSTRING_PTR(tmp), RSTRING_END(tmp), valenc) != 1) {
                         rb_raise(rb_eArgError, "%%c requires a character");
                     }
-                    c = rb_enc_codepoint_len(RSTRING_PTR(tmp), RSTRING_END(tmp), &n, enc);
+                    c = rb_enc_codepoint_len(RSTRING_PTR(tmp), RSTRING_END(tmp), &n, valenc);
                     RB_GC_GUARD(tmp);
                 }
                 else {
diff --git a/test/ruby/test_m17n.rb b/test/ruby/test_m17n.rb
index c00bf59e18..2c6fcee004 100644
--- a/test/ruby/test_m17n.rb
+++ b/test/ruby/test_m17n.rb
@@ -892,6 +892,8 @@ class TestM17N < Test::Unit::TestCase
     assert_raise(Encoding::CompatibilityError) {
       "%s%s" % [s("\xc2\xa1"), e("\xc2\xa1")]
     }
+
+    "%c" % "\u3042".encode('Windows-31J')
   end
 
   def test_sprintf_p