Re: libc/printf bug

"bill pursell" <bill.pursell@xxxxxxxxx> writes:

The following code exhibits unexpected behavior. Either it's
a bug in libc, or the author (me) is blind as a bat. Am I missing
something here, or is something horribly wrong? It appears
that printf is mangling the address unless the second argument
gets cast. I don't see that the cast should have any effect at all
on the output. Any thoughts?

[tmp]$ cat printf_bug.c

int
main()
{

float a=0;

printf("%p\n", &a);
printf("%x %p\n", a, &a);
printf("%x %p\n", (int)a, &a);
}
[tmp]$ ./a.out
0xfefb6764
0 (nil)
0 0xfefb6764
[tmp]$

When passed to a function with variable arguments, float arguments are
promoted to double. A double is usually 64 bits, and the %x format
uses only 32 of these, leaving the remaining 32 for the %p.

--
Måns Rullgård
mru@xxxxxxxxxxxxx
.

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