# \[Bug:trunk\] rubyspec: StringIO#ungetc when passed \[char\] pads with \\000 when the current position i

**URL:** <https://www.ruby-forum.com/t/bug-trunk-rubyspec-stringio-ungetc-when-passed-char-pads-with-000-when-the-current-position-i/182623>\
**Category:** Development\
**Created:** [January 31, 2010, 11:24am UTC](https://www.ruby-forum.com/t/bug-trunk-rubyspec-stringio-ungetc-when-passed-char-pads-with-000-when-the-current-position-i/182623 "2010-01-31T11:24:19Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [January 31, 2010, 11:24am UTC](https://www.ruby-forum.com/t/bug-trunk-rubyspec-stringio-ungetc-when-passed-char-pads-with-000-when-the-current-position-i/182623/1 "2010-01-31T11:24:19Z")

</div>

stringio e$B$N%a%s%F%J$N$J$+$@$5$s!"$b$7$/$O$^$D$b$H$5$se(B  
e$B1sF#$G$9!#e(B

stringio e$B$K4X$7$F!"%P%C%U%!=\*C\<$h$j@h$Ke(B pos e$B$r9g$o$;$?\>uBV$Ge(B  
StringIO#ungetc e$B$r8F$s$@;~$N5sF0$,e(B 1.8 e$B$He(B 1.9  
e$B$G0c$$$^$9!#e(B

# 1.8 e$B$G$O4V$,e(B \0 e$B$GKd$a$i$l$ke(B

$ ruby18 -rstringio -e ’  
io = StringIO.new(“1234”)  
io.pos = 15  
io.ungetc(?A)  
p io.string  
’  
“1234\000\000\000\000\000\000\000\000\000\000A”

# 1.9 e$B$G$ONc30$K$J$ke(B

$ ./ruby -rstringio -e ’  
io = StringIO.new(“1234”)  
io.pos = 15  
io.ungetc(?A)  
p io.string  
’  
-e:4:in `ungetc': index 14 out of string (IndexError) from -e:4:in`’

r13261 e$B$,860x$N$h$&$G$9!#$3$N5sF0$NJQ99$rA@$C$?$b$N$G$O$J$$e(B  
e$B$h$&$J5$$,$7$^$9$,!"$$$+$,$G$7$g$&$+!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [February 4, 2010, 7:46pm UTC](https://www.ruby-forum.com/t/bug-trunk-rubyspec-stringio-ungetc-when-passed-char-pads-with-000-when-the-current-position-i/182623/2 "2010-02-04T19:46:13Z")

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e$B1sF#$G$9!#e(B

2010e$BG/e(B1e$B7ne(B31e$BF|e(B19:21 Yusuke ENDOH [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> ’  
> -e:4:in `ungetc': index 14 out of string (IndexError) from -e:4:in `’
> 
> r13261 e$B$,860x$N$h$&$G$9!#$3$N5sF0$NJQ99$rA@$C$?$b$N$G$O$J$$e(B  
> e$B$h$&$J5$$,$7$^$9$,!"$$$+$,$G$7$g$&$+!#e(B

e$B@.@%$5$s$N4F=$$N$b$H!"%Q%C%A$r=q$$$F$_$^$7$?!#e(B  
e$BH?BP$,$J$1$l$P%3%_%C%H$7$F$7$^$$$^$9!#e(B

diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c  
index f193c6e…faf974e 100644  
— a/ext/stringio/stringio.c  
+++ b/ext/stringio/stringio.c  
@@ -725,17 +725,26 @@ strio\_ungetc(VALUE self, VALUE c)  
c = rb\_str\_conv\_enc(c, enc2, enc);  
}  
}

- /\* get logical position \*/
- lpos = 0; p = RSTRING\_PTR(ptr-\>string); pend = p + ptr-\>pos;
- for (;😉 {
- clen = rb\_enc\_mbclen(p, pend, enc);
- if (p+clen \>= pend) break;
- p += clen;
- lpos++;

- if (RSTRING\_LEN(ptr-\>string) \< ptr-\>pos) {
- long len = RSTRING\_LEN(ptr-\>string);
- rb\_str\_resize(ptr-\>string, ptr-\>pos - 1);
- memset(RSTRING\_PTR(ptr-\>string) + len, 0, ptr-\>pos - len - 1);
- rb\_str\_concat(ptr-\>string, c);
- ptr-\>pos–;
- }
- else {
- /\* get logical position \*/
- lpos = 0; p = RSTRING\_PTR(ptr-\>string); pend = p + ptr-\>pos;
- for (;😉 {
- 

```
 clen = rb_enc_mbclen(p, pend, enc);

```

- 

```
 if (p+clen >= pend) break;

```

- 

```
 p += clen;

```

- 

```
 lpos++;

```

- }
- clen = p - RSTRING\_PTR(ptr-\>string);
- rb\_str\_update(ptr-\>string, lpos, ptr-\>pos ? 1 : 0, c);
- ptr-\>pos = clen;  
}

- clen = p - RSTRING\_PTR(ptr-\>string);

- rb\_str\_update(ptr-\>string, lpos, ptr-\>pos ? 1 : 0, c);

- ptr-\>pos = clen;

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [February 5, 2010, 6:09pm UTC](https://www.ruby-forum.com/t/bug-trunk-rubyspec-stringio-ungetc-when-passed-char-pads-with-000-when-the-current-position-i/182623/3 "2010-02-05T18:09:41Z")

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e$B%A%1%C%He(B #2696 e$B$,99?7$5$l$^$7$?!#e(B (by Yusuke E.)

e$B%9%F!\<%?%9e(B Assignede$B$+$ie(BClosede$B$KJQ99e(B  
e$B?JD=e(B % 0e$B$+$ie(B100e$B$KJQ99e(B

This issue was solved with changeset r26588.  
Yusuke, thank you for reporting this issue.  
Your contribution to Ruby is greatly appreciated.  
May Ruby be with you.

* * *

[http://redmine.ruby-lang.org/issues/show/2696](http://redmine.ruby-lang.org/issues/show/2696)