New: scanf man page is misleading re out-of-range integer conversions
https://bugzilla.kernel.org/show_bug.cgi?id=61511
Bug ID: 61511
Summary: scanf man page is misleading re out-of-range integer
conversions
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
Assignee: documentation_man-pages-ztI5WcYan/[email protected]
Reporter: [email protected]
Regression: No
Unless I'm missing it, the scanf man page doesn't really specifically address the result of an out-of-range integer conversion -- e.g. sscanf("9999999999999999999999999999999", "%d", &i).
The ERRORS section, however, says this:
ERANGE The result of an integer conversion would exceed the size that
can be stored in the corresponding integer type.
This is definitely *not* the behavior that I'm seeing. Instead, sscanf is returning 1 and -1 is assigned to i.
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A message that is not in the archive (sent off-list or not yet received): bug-61511-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/
Am 16.09.2013 22:04, schrieb bugzilla-daemon-590EEB7GvNiWaY/[email protected]:
Quoted 1 line
sscanf("9999999999999999999999999999999", "%d", &i).
please try this code:
#include <stdio.h>
#include <errno.h>
int main()
{
int ret,i;
ret=sscanf("9999999999999999999999999999999", "%d", &i);
perror("scanf");
printf("ret=%d i=%d\n",ret,i);
return 0;
}re,
wh
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[Bug 61511] scanf man page is misleading re out-of-range integer conversions
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=61511
--- Comment #1 from walter <[email protected]> ---
Am 16.09.2013 22:04, schrieb bugzilla-daemon-590EEB7GvNiWaY/[email protected]:
Quoted 1 line
sscanf("9999999999999999999999999999999", "%d", &i).
please try this code:
#include <stdio.h>
#include <errno.h>
int main()
{
int ret,i;
ret=sscanf("9999999999999999999999999999999", "%d", &i);
perror("scanf");
printf("ret=%d i=%d\n",ret,i);
return 0;
}re,
wh
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[Bug 61511] scanf man page is misleading re out-of-range integer conversions
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=61511
--- Comment #2 from Ian Pilcher <[email protected]> --- (In reply to walter from comment #1)
Quoted 5 lines
please try this code:
#include <
stdio.h>
#include <errno.h>
intmain()
Quoted 7 lines
{
int ret,i;
ret=sscanf("9999999999999999999999999999999", "%d", &i);
perror("scanf");
printf("ret=%d i=%d\n",ret,i);
return 0;
}scanf: Numerical result out of range
ret=1 i=-1
So it is setting errno, but it's still returning 1. That's just weird. (But allowed, since the behavior is undefined in this case.)
Perhaps the ERANGE section could note that it can occur even when the function does not return EOF.
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[Bug 61511] scanf man page is incomplete re out-of-range integer conversions
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=61511
Ian Pilcher <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|scanf man page is |scanf man page is
|misleading re out-of-range |incomplete re out-of-range
|integer conversions |integer conversionsSignature · 6 lines
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[Bug 61511] scanf man page is incomplete re out-of-range integer conversions
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=61511
Jon Harper <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]
--- Comment #3 from Jon Harper <[email protected]> --- strtod(3) has the following note:
NOTES
Since 0 can legitimately be returned on both success and failure, the
calling program should set errno to 0 before the call, and
then determine if an error occurred by checking whether errno has a
nonzero value after the call.
Maybe add the same note to scanf(3) ?
Also, the example program from scanf(3) is:
char *p;
int n;
errno = 0;
n = scanf("%m[a-z]", &p);
if (n == 1) {
printf("read: %s\n", p);
free(p);
} else if (errno != 0) {
perror("scanf");
} else {
fprintf(stderr, "No matching characters\n");
}which suggests checking for the return value of scanf before checking for errno, which is wrong in the integer overflow case as scanf returns 1. Change the order of the checks ?
Also, for scanf, it doesn't set i to a constant value (adapting the example program to read an int):
jon@zog:~$ cat dez.c #include "stdlib.h" #include "stdio.h" #include "errno.h"
int main() {
int res;
int n;
errno = 0;
n = scanf("%d", &res);
if (n == 1) {
printf("read: %d\n", res);
} else if (errno != 0) {
perror("scanf");
} else {
fprintf(stderr, "No matching characters\n");
}
}jon@zog:~$ for ((i=0; i<30; i++)); do echo "$((10**i -1))" | ./dez; done read: 0 read: 9 read: 99 read: 999 read: 9999 read: 99999 read: 999999 read: 9999999 read: 99999999 read: 999999999 read: 1410065407 read: 1215752191 read: -727379969 read: 1316134911 read: 276447231 read: -1530494977 read: 1874919423 read: 1569325055 read: -1486618625 read: -1981284353 read: 1661992959 read: -559939585 read: -1304428545 read: -159383553 read: -1593835521 read: 1241513983 read: -469762049 read: -402653185 read: 268435455 read: -1610612737
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