考虑以下程序：
#include <stdexcept>
#include <stdio.h>
#include <memory>
#include <list>
class Foo {
public:
Foo(){
if (s_ct==0) {throw std::bad_alloc();}
--s_ct;
fprintf(stderr, "ctor %p\n", this);
}
~Foo(){
fprintf(stderr, "dtor %p\n", this);
}
private:
static int s_ct;
};
int Foo::s_ct = 2;
int main(){
try {
std::list<std::shared_ptr<Foo>> l = {
std::make_shared<Foo>(),
std::make_shared<Foo>(),
std::make_shared<Foo>()
};
} catch (std::bad_alloc&) {
fprintf(stderr, "caught exception.\n");
}
fprintf(stderr, "done.\n");
return 0;
}
编译方式如下：
[little:~] $ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609
Copyright (C) 2015 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.
[little:~] $ g++ --std=c++14 -o list_init list_init.cc
[little:~] $
输出结果为：
[little:~] $ ./list_init
ctor 0x1294c30
ctor 0x1294c50
caught exception.
done.
[little:~] $
这似乎违反了std::make_shared的一个关键目的 - 即，如果语句中的另一个表达式抛出异常，则由于它被完全构造的共享指针对象包装，因此共享对象将得到适当的销毁。
这里Clang做了我想要的事情：
[little:~] $ clang++ --version
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
[little:~] $ clang++ --std=c++14 -o foo list_init.cc
[little:~] $ ./foo
ctor 0x1dfec30
ctor 0x1dfec50
dtor 0x1dfec50
dtor 0x1dfec30
caught exception.
done.
[little:~] $
那么这是GCC的bug，还是我需要修复我的程序？