Hello, I unintentionally stumbled upon some strange behaviour that
occurred due to a typo.
I reproduced the behaviour where an object (std::string in my case) can
be passed to a function by reference, uninitialized, WITHOUT a compiler
warning.
Changing the code to pass the object by value DOES emit the warning.
I don't think the compiled code is incorrect, it segfaults presumably
due to uninitialized members.
I understand there may seldom be a reason to use uninitialized objects,
so "don't do that," but as I said this was unintentional and it seems
that it should have generated a warning, which have saved some
head-scratching.
Code to reproduce:
#include <string>
std::string f(std::string &s) {
s.append("x");
return s;
}
int main() {
std::string a = f(a);
}
Compile and run (no warning):
$ g++ -o uninit_obj uninit_obj.cpp -std=c++23 -Wall -Wpedantic -Wextra
&& ./uninit_obj
Segmentation fault (core dumped)
No difference whether using -O0 (or 1 2 3)
If I change the function to pass by value, std::string f(std::string s),
and rerun, I get the expected compiler warning:
$ g++ -o uninit_obj uninit_obj.cpp -std=c++23 -Wall -Wpedantic -Wextra
&& ./uninit_obj
uninit_obj.cpp: In function 'int main()':
uninit_obj.cpp:7:22: warning: 'a' may be used uninitialized
[-Wmaybe-uninitialized]
7 | std::string a = f(a);
[...]
terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
Aborted (core dumped)
Output from g++ -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/gcc13/libexec/gcc/x86_64-pc-linux-gnu/13.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-13.2.0/configure --disable-multilib
--enable-languages=c,c++ --prefix=/usr/local/gcc13 --program-suffix=-13
--enable-libstdcxx-backtrace=yes
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.2.0 (GCC)
Thanks
