[Mingw-notify] [ mingw-Bugs-1083721 ] Broken snprintf().

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Bugs item #1083721, was opened at 2004-12-11 20:10
Message generated for change (Comment added) made by aaronwl
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=102435&aid=1083721&group_id=2435

Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: William G. Davis (william_g_davis)
Assigned to: Nobody/Anonymous (nobody)
Summary: Broken snprintf().

Initial Comment:
Hi guys.

This was brough to my attention by a few people. It
looks like snpritnf() is slightly broken. Here's a few
examples along with the output they produced:
--------------------
#include <stdio.h>

int main(void)
{
	char string[10];
	char string2[10];
	char string3[12];
	int rv;

	rv = snprintf(string, sizeof(string), "%s", "longer
than ten");
	printf("[%s] (%d)\n", string, rv);

	rv = snprintf(string2, sizeof(string2), "%s", "shorter");
	printf("[%s] (%d)\n", string2, rv);

	rv = snprintf(
		string3, sizeof(string3), "%s%d%s", "longer", 7777,
"than ten"
	);
	printf("[%s] (%d)\n", string3, rv);

	return 0;
}
--------------------
[longer tha] (-1)
[shorter] (7)
[longer7777th_²s] (-1)
--------------------

Here's what C99 has to say about snprintf():

"Description

"The snprintf function is equivalent to fprintf, except
that the output
is written into an array (specified by arguments)
rather than to a
stream. If n is zero, nothing is written, and s may be
a null
pointer. Otherwise, output characters beyond the n-1st
are discarded
rather than being written to the array, and a null
character is written
at the end of the characters actually written into the
array. If copying
takes place between objects that overlap, the behavior
is undefined.

"Returns

"The snprintf function returns the number of characters
that would have
been written had n been sufficiently large, not
counting the terminating
null character, or a negative value if an encoding
error occurred. Thus,
the null-terminated output has been completely written
if and only if
the returned value is nonnegative and less than n."

Which means that if the input is larger than the size
argument, then only size-1 characters should be
written, and regardless, a NULL terminator should
*always* be written to the end of the destination buffer.

Here's the version infomration:
Configured with: ../gcc/configure --with-gcc
--with-gnu-ld --with-gnu-as --host
mingw32 --target=mingw32 --prefix=/mingw
--enable-threads --disable-nls --enabl
-languages=c,c++,f77,objc,ada,java
--disable-win32-registry --disable-shared --
nable-sjlj-exceptions --enable-libgcj
--disable-java-awt --without-x --enable-j
va-gc=boehm --disable-libgcj-debug --enable-interpreter
--enable-hash-synchroni
ation
Thread model: win32
gcc version 3.3.1 (mingw special 20030804-1)

Thanks.

----------------------------------------------------------------------

Comment By: Aaron W. LaFramboise (aaronwl)
Date: 2004-12-11 21:10

Message:
Logged In: YES 
user_id=1040098

For comparison, here is the output on my machine, using
msvcrt 7.0.2600.2180.

[longer th] (15)
[shorter] (7)
[longer7777t] (18)

Find msvcrt.dll in windows\system32 and check its version on
the property tab.

I would suspect this difference comes from an older version
of this runtime using a pre-standard snprintf
implementation.  (Historical UNIX implementations also
disagree with regards to this function.)


----------------------------------------------------------------------

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