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* [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time
@ 2021-08-10 19:04 prasantabehera at hotmail dot com
2021-08-10 19:09 ` [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected) pinskia at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: prasantabehera at hotmail dot com @ 2021-08-10 19:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
Bug ID: 101850
Summary: Initialising a std::string variable to itself does not
fail at compile time, but throws std::bad_alloc at run
time
Product: gcc
Version: 8.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: prasantabehera at hotmail dot com
Target Milestone: ---
Version info:
=============
~$ g++ --version
g++ (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
~$ gcc --version
gcc (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Sample Program:
===============
~$ cat t.cpp
#include <string>
int main() {
std::string s = s;
return 0;
}
Problem Description:
====================
The above program tries to initialise a string with itself which is wrong!
However g++ does not show any compile time error, but the resulting binary
fails at run time throwing std::bad_alloc as shown below.
~$ g++ t.cpp
~$ ./a.out
terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
Aborted (core dumped)
gcc however shows a link time error which is slightly better.
~$ gcc t.cpp
/tmp/cc30YkgH.o: In function `main':
t.cpp:(.text+0x27): undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char>
>::basic_string(std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> > const&)'
t.cpp:(.text+0x38): undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >::~basic_string()'
collect2: error: ld returned 1 exit status
I think the coding error should be caught at the compile time by g++.
Also, the problem is same with any generic C++ class/struct:
#include <string>
struct M {
std::string s;
};
int main() {
// std::string s = s;
M m = m;
return 0;
}
Also checked with g++ version 7.5.0, to see the same behavior.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
@ 2021-08-10 19:09 ` pinskia at gcc dot gnu.org
2021-08-10 19:11 ` pinskia at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-10 19:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In GCC 11+ we start to warn about this code with -W -Wall:
<source>: In function 'int main()':
<source>:5:19: warning: 's' may be used uninitialized [-Wmaybe-uninitialized]
5 | std::string s = s;
| ^
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
2021-08-10 19:09 ` [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected) pinskia at gcc dot gnu.org
@ 2021-08-10 19:11 ` pinskia at gcc dot gnu.org
2021-08-10 19:42 ` redi at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-10 19:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Depends on| |48829
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
See PR 48829 also.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48829
[Bug 48829] g++ no warning initializing a variable using itself
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
2021-08-10 19:09 ` [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected) pinskia at gcc dot gnu.org
2021-08-10 19:11 ` pinskia at gcc dot gnu.org
@ 2021-08-10 19:42 ` redi at gcc dot gnu.org
2021-08-10 19:48 ` prasantabehera at hotmail dot com
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-08-10 19:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Prasanta Behera from comment #0)
> Version info:
> =============
> ~$ g++ --version
> g++ (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
> Copyright (C) 2018 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> ~$ gcc --version
> gcc (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0
> Copyright (C) 2018 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> Sample Program:
> ===============
> ~$ cat t.cpp
> #include <string>
>
> int main() {
> std::string s = s;
> return 0;
> }
>
> Problem Description:
> ====================
> The above program tries to initialise a string with itself which is wrong!
Yes, it's undefined behaviour.
> However g++ does not show any compile time error, but the resulting binary
> fails at run time throwing std::bad_alloc as shown below.
That's one way that undefined behaviour can manifest itself. You cannot expect
to get a compile time error for all cases of undefined behaviour, that's why
it's undefined.
> ~$ g++ t.cpp
> ~$ ./a.out
> terminate called after throwing an instance of 'std::bad_alloc'
> what(): std::bad_alloc
> Aborted (core dumped)
>
> gcc however shows a link time error which is slightly better.
>
> ~$ gcc t.cpp
> /tmp/cc30YkgH.o: In function `main':
> t.cpp:(.text+0x27): undefined reference to `std::__cxx11::basic_string<char,
> std::char_traits<char>, std::allocator<char>
> >::basic_string(std::__cxx11::basic_string<char, std::char_traits<char>,
> std::allocator<char> > const&)'
> t.cpp:(.text+0x38): undefined reference to `std::__cxx11::basic_string<char,
> std::char_traits<char>, std::allocator<char> >::~basic_string()'
> collect2: error: ld returned 1 exit status
No, this is just because gcc doesn't link to the C++ runtime which is needed to
use std::string. You will get the same link error for a correct program, it has
absolutely nothing to do with the bug in your code.
> I think the coding error should be caught at the compile time by g++.
It is caught, by a warning.
In the general case, turning all such mistakes into errors is impossible:
const std::string& func(const std::string&);
std::string s = func(s);
The compiler cannot know whether func has undefined behaviour or not. It could
be defined like this, which would be OK:
const std::string& func(const std::string& /*unused*/) {
static std::string str = "a string with static storage duration";
}
Or it could be defined like this, which would be equivalent to your example:
const std::string& func(const std::string& s) {
return s;
}
tl;dr it is not reasonable to expect to always get a compile time error for
undefined behaviour, it's the programmer's responsibility to avoid undefined
behaviour. COmpiler warnings can help, if you enable them and pay attention to
them.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
` (2 preceding siblings ...)
2021-08-10 19:42 ` redi at gcc dot gnu.org
@ 2021-08-10 19:48 ` prasantabehera at hotmail dot com
2021-08-10 19:51 ` redi at gcc dot gnu.org
2021-08-10 20:00 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: prasantabehera at hotmail dot com @ 2021-08-10 19:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
--- Comment #4 from Prasanta Behera <prasantabehera at hotmail dot com> ---
FWIW clang++ does produce these warnings:
~$ cat t.cpp
#include <string>
class M {
std::string s;
public:
M(std::string t) : s(t) {}
};
int main() {
std::string s = s;
M m = m;
return 0;
}
~$ clang++ t.cpp
t.cpp:11:19: warning: variable 's' is uninitialized when used within its own
initialization [-Wuninitialized]
std::string s = s;
~ ^
t.cpp:12:9: warning: variable 'm' is uninitialized when used within its own
initialization [-Wuninitialized]
M m = m;
~ ^
2 warnings generated.
~$ clang++ --version
clang version 10.0.0-4ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Similar warnings for g++ too will help a lot!
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
` (3 preceding siblings ...)
2021-08-10 19:48 ` prasantabehera at hotmail dot com
@ 2021-08-10 19:51 ` redi at gcc dot gnu.org
2021-08-10 20:00 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-08-10 19:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=18635
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Did you read comment 1?
GCC already warns. You're using GCC 8.4.0 which is old and unsupported.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected)
2021-08-10 19:04 [Bug c++/101850] New: Initialising a std::string variable to itself does not fail at compile time, but throws std::bad_alloc at run time prasantabehera at hotmail dot com
` (4 preceding siblings ...)
2021-08-10 19:51 ` redi at gcc dot gnu.org
@ 2021-08-10 20:00 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-08-10 20:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101850
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Target Milestone|--- |11.0
Status|UNCONFIRMED |RESOLVED
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
extern "C" char* strdup(const char*);
extern "C" void free(void*);
namespace std
{
struct string
{
string() { }
string(string const& s) : data(strdup(s.data)) { }
string& operator=(string const& s) {
free(data);
strdup(s.data);
return *this;
}
~string() { free(data); }
char* data = nullptr;
};
}
class M {
std::string s;
public:
M(std::string t) : s(t) {}
};
int main() {
M m = m;
}
This started to warn with r11-959 "Implement a solution for PR middle-end/10138
and PR middle-end/95136."
I think this can be considered FIXED for GCC 11.
^ permalink raw reply [flat|nested] 7+ messages in thread
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2021-08-10 19:09 ` [Bug c++/101850] Initialising a struct/class variable to itself does not fail at compile time (but throws std::bad_alloc at run time, as expected) pinskia at gcc dot gnu.org
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