std::seed_seq编译错误(GCC错误?）

std::seed_seq compilation error (GCC bug?)

本文关键字：错误 GCC 编译 seed seq std      更新时间：2023-10-16

我有以下几行代码，GCC的最新版本无法编译。我确信它甚至没有发出警告信息。

seed_seq.cpp:

void func()
{
std::mt19937_64 engine;
std::hash<std::thread::id> hasher;
uint64_t rdSeed, threadID, now;
try
{
std::random_device rd;
if (rd.entropy())
rdSeed = rd();
else
rdSeed = 0;
}
catch (std::exception &)
{
rdSeed = 0;
}
threadID = hasher(std::this_thread::get_id());
now = std::chrono::system_clock::now().time_since_epoch().count();
engine.seed(std::seed_seq{ rdSeed, threadID, now });
}

命令：gcc -std=c++11 -c seed_seq.cpp -o seed_seq.o

无法编译的GCC版本：

  • gcc(gcc)6.3.1 20161221(Red Hat 6.3.1-1)
  • gcc(Ubuntu 5.4.0-6ubuntu1~16.04.4)5.4.0 20160609

VS2013更新5没有抱怨。肯定是GCC的错？

我不记得GCC的有效版本了。很抱歉

错误：

seed_seq.cpp: In function ‘void func()’:
seed_seq.cpp:28:19: error: invalid initialization of non-const reference of type ‘std::seed_seq&’ from an rvalue of type ‘std::seed_seq’
engine.seed(std::seed_seq{ rdSeed, threadID, now });
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/6.3.1/random:51:0,
from seed_seq.cpp:2:
/usr/include/c++/6.3.1/bits/random.tcc:353:7: note:   initializing argument 1 of ‘typename std::enable_if<std::is_class<_Sseq>::value>::type std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>::seed(_Sseq&) [with _Sseq = std::seed_seq; _UIntType = long unsigned int; long unsigned int __w = 64ul; long unsigned int __n = 312ul; long unsigned int __m = 156ul; long unsigned int __r = 31ul; _UIntType __a = 13043109905998158313ul; long unsigned int __u = 29ul; _UIntType __d = 6148914691236517205ul; long unsigned int __s = 17ul; _UIntType __b = 8202884508482404352ul; long unsigned int __t = 37ul; _UIntType __c = 18444473444759240704ul; long unsigned int __l = 43ul; _UIntType __f = 6364136223846793005ul; typename std::enable_if<std::is_class<_Sseq>::value>::type = void]’
mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
__s, __b, __t, __c, __l, __f>::
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

更新

在系统的dnf.log上发现了这个。不确定哪一个是我在项目中使用的。。。

Nov 01 18:17:41 DEBUG ---> Package gcc-gdb-plugin.x86_64 6.2.1-2.fc24 will be installed
Nov 01 18:17:42 DEBUG ---> Package gcc.x86_64 5.3.1-6.fc23 will be upgraded
Nov 01 18:17:42 DEBUG ---> Package gcc.x86_64 6.2.1-2.fc24 will be an upgrade
Nov 01 18:17:42 DEBUG ---> Package gcc-c++.x86_64 5.3.1-6.fc23 will be upgraded
Nov 01 18:17:42 DEBUG ---> Package gcc-c++.x86_64 6.2.1-2.fc24 will be an upgrade
Nov 01 18:17:42 DEBUG ---> Package libgcc.x86_64 5.3.1-6.fc23 will be upgraded
Nov 01 18:17:42 DEBUG ---> Package libgcc.x86_64 6.2.1-2.fc24 will be an upgrade                                                  
Nov 02 11:03:25 DEBUG ---> Package gcc-debuginfo.x86_64 6.2.1-2.fc24 will be installed
Nov 02 11:03:25 DEBUG ---> Package gcc-base-debuginfo.x86_64 6.2.1-2.fc24 will be installed
Jan 04 09:59:34 DEBUG ---> Package gcc.x86_64 6.2.1-2.fc24 will be upgraded
Jan 04 09:59:34 DEBUG ---> Package gcc.x86_64 6.3.1-1.fc24 will be an upgrade
Jan 04 09:59:34 DEBUG ---> Package gcc-gdb-plugin.x86_64 6.2.1-2.fc24 will be upgraded
Jan 04 09:59:34 DEBUG ---> Package gcc-gdb-plugin.x86_64 6.3.1-1.fc24 will be an upgrade
Jan 04 09:59:34 DEBUG ---> Package gcc-c++.x86_64 6.2.1-2.fc24 will be upgraded
Jan 04 09:59:34 DEBUG ---> Package gcc-c++.x86_64 6.3.1-1.fc24 will be an upgrade
Jan 04 09:59:34 DEBUG ---> Package libgcc.x86_64 6.2.1-2.fc24 will be upgraded
Jan 04 09:59:34 DEBUG ---> Package libgcc.x86_64 6.3.1-1.fc24 will be an upgrade

很明显，您传递给engine.seed()的参数就是问题所在
我建议你看看

种子()

让我们简单了解一下原因
正如您所看到的，有两种方法可以调用由以下定义的seed()：

void seed( result_type value = default_seed );

和

void seed( Sseq& seq );

如果你担心gcc中有一个bug，那么我认为你不应该
事实上Clang 3.9.1(只是提到一个版本)也给出了类似的错误：

Start
prog.cc:32:12: error: no matching member function for call to 'seed'
engine.seed(std::seed_seq{ rdSeed, threadID, now });
~~~~~~~^~~~
/opt/wandbox/clang-3.9.1/include/c++/v1/random:2116:10: note: candidate function not viable: no known conversion from 'std::seed_seq' to 'result_type' (aka 'unsigned long') for 1st argument
void seed(result_type __sd = default_seed);
^
/opt/wandbox/clang-3.9.1/include/c++/v1/random:2124:9: note: candidate function [with _Sseq = std::__1::seed_seq] not viable: expects an l-value for 1st argument
seed(_Sseq& __q)
^
1 error generated.
1
Finish

并准确地指出问题所在
我发现gcc和clang不太可能有相同的错误，但一切都有可能
要了解如何将seed()与std::seed_seq组合调用，您应该查看下面的seed()，它有一个类似的例子
问题可以解决，正如您已经提到的

std::seed_seq seq{ rdSeed, threadID, now };
engine.seed(seq);

或者(这是一种冗长的方式，我可能不会这么做)：

std::seed_seq seq{ rdSeed, threadID, now };
std::seed_seq& pr = seq;
engine.seed(pr);

要了解更多关于这种情况/错误的信息，我建议您阅读以下SO帖子：
类型'；的非常量引用的初始化无效；int&#39；从类型为'；int'；

正如@Ashe the human在评论中指出的那样，VS2013允许它编译，因为它是默认启用的语言扩展：它应该发出警告，让人们知道。您可以在这里阅读更多关于它的信息：
绑定到临时Visual Studio bug的非常量引用？

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