[Bug c++/90005] New: No error produced for the wrong type of string used in gcc >= 5.0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90005
Bug ID: 90005
Summary: No error produced for the wrong type of string used in
gcc >= 5.0
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pawel.wrobel at nielsen dot com
Target Milestone: ---
Hello,
I have the question regarding the following behaviour of gcc 8.3 (it behaves
the same way from version 5.0 up to 8.3 - when I tested with the
https://gcc.godbolt.org/).
When I compile following program (it has an obvious omission - missing .c_str()
conversion of std::string to char*)
#include
#include
int main()
{
std::string txt("there");
printf("Hello %s ! \n", txt);
}
On the gcc 4.9 and before - it correctly notifies me with an error like :
: In function 'int main()':
:6:30: error: cannot pass objects of non-trivially-copyable type
'std::string {aka class std::basic_string}' through '...'
printf("Hello %s ! \n", txt);
Compiler returned: 1
However, starting from the gcc 5.0 and above (gcc 8.3 included) - no error is
generated - and the binary is being produced. It obviously prints the garbage
when run ("Hello (`e !"). So lack of the error should be considered as an bug ?
Or maybe do I need to provide some special flag for this error message to
appear and stop the compilation in gcc 5.0 and above ?
Both the gcc <= 4.9 works correctly here (and the newer clang compilers also
point out this error correctly). Can I make the gcc >= 5.0 to generate an error
here with some flag ?
[Bug c++/90005] No error produced for the wrong type of string used in gcc >= 5.0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90005
--- Comment #2 from Pawel ---
Hi,
Thanks,
Adding -Wformat indeed show up a waring here :
$ g++ -Wformat main.cpp -o out
main.cpp: In function ‘int main()’:
main.cpp:6:30: warning: format ‘%s’ expects argument of type ‘char*’, but
argument 2 has type ‘std::string* {aka std::basic_string*}’ [-Wformat=]
printf("Hello %s ! \n", txt);
I can make it into an error using the -Werror flag then - however - that seems
to be too strict. In the actual, real-scenario code, I think, I cannot afford
to use the -Werror flag globally - since it will turn many of otherwise
harmless warnings into errors.
Is there a reason why this is considered to be 'just a harmless warning' by
newer(>=5.0) gcc - whereas other gcc(<5.0)/complers consider this a "hard
problem" (doing this omission changes program into printing the complete
garbage, so just a warning seems to be a little too soft there)...
The warning/error message also is so different between gcc versions here..
[Bug c++/90005] No error produced for the wrong type of string used in gcc >= 5.0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90005 --- Comment #6 from Pawel --- Hi, Thanks for the explanation. Indeed, for example, the clang does not support the non-POD(ex. std::string) to variadic function - as : error: cannot pass non-trivial object of type 'std::__cxx11::string' (aka 'basic_string') to variadic function;
[Bug c++/90005] No error produced for the wrong type of string used in gcc >= 5.0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90005 --- Comment #7 from Pawel --- The "-Werror=format" solution seems to work for me - it triggers the error here (missing .c_str()) even for the gcc >= 5.0 - leaving all the other, non-related warnings untouched. Thanks
[Bug c++/90005] No error produced for the wrong type of string used in gcc >= 5.0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90005 --- Comment #9 from Pawel --- Hello Eric, Thank You so much for this answer - in our case that turned out also to be really useful. We took the "-Werror=conditionally-supported" version - to trigger an error in our custom variadic function - as we really do not want the non-POD(std::string in our case) argument there - and we prefer having the error visible, when someone accidentally use std::string instead of char* in the large codebase. Thanks !
