使用constexpr initializer_list数组在MSVC崩溃，GCC/Clang正常

问题现象 #

一段用于单元测试的C++代码，在GCC和Clang下可正常编译运行，但在Win10系统使用MSVC 19.38.33133编译后，无论是否启用AddressSanitizer，运行时都会崩溃。

示例代码 #

#include <initializer_list>
#include <iostream>
#include <string_view>
#include <vector>

using namespace std::string_view_literals;

constexpr std::initializer_list<std::string_view> data[] {
    {},
    {
        "aa"sv,
        "bb"sv,
    },
    {
        "cc"sv,
        "dd"sv,
        "ee"sv,
    },
};

std::vector<std::string> banHashesDataGenerator(size_t index)
{
    if (index >= std::size(data)) {
        throw std::invalid_argument { "index out of range" };
    }
    std::vector<std::string> result;
    for (auto& item : data[index]) {
        result.emplace_back(std::string { item });
    }
    return result;
}

int main()
{
    for (auto& x : banHashesDataGenerator(1)) {
        std::cout << x << '\n';
    }

    return 0;
}

编译及运行日志 #

C:\Users\marek r\Downloads>cl /std:c++20 /EHcs bug.cpp /fsanitize=address /Zi
Microsoft (R) C/C++ Optimizing Compiler Version 19.38.33133 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

bug.cpp
Microsoft (R) Incremental Linker Version 14.38.33133.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:bug.exe
/InferAsanLibs
/debug
bug.obj

C:\Users\marek r\Downloads>bug.exe
=================================================================
==21384==ERROR: AddressSanitizer: access-violation on unknown address 0x000000000000 (pc 0x7ff62bc718e1 bp 0x000000000000 sp 0x008189cff9a0 T0)
==21384==The signal is caused by a READ memory access.
==21384==Hint: address points to the zero page.
    #0 0x7ff62bc718e0 in std::basic_string<char, struct std::char_traits<char>, class std::allocator<char>>::basic_string<char, struct std::char_traits<char>, class std::allocator<char>><class std::basic_string_view<char, struct std::char_traits<char>>, 0>(class std::basic_string_view<char, struct std::char_traits<char>> const &, class std::allocator<char> const &) (C:\Users\marek r\Downloads\bug.exe+0x1400018e0)
    #1 0x7ff62bc7140d in banHashesDataGenerator(unsigned __int64) (C:\Users\marek r\Downloads\bug.exe+0x14000140d)
    #2 0x7ff62bc715a8 in main (C:\Users\marek r\Downloads\bug.exe+0x1400015a8)
    #3 0x7ff62bcb9bbb in invoke_main D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:78
    #4 0x7ff62bcb9bbb in __scrt_common_main_seh D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
    #5 0x7ffd2b8f7343  (C:\WINDOWS\System32\KERNEL32.DLL+0x180017343)
    #6 0x7ffd2cba26b0  (C:\WINDOWS\SYSTEM32\ntdll.dll+0x1800526b0)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: access-violation (C:\Users\marek r\Downloads\bug.exe+0x1400018e0) in std::basic_string<char, struct std::char_traits<char>, class std::allocator<char>>::basic_string<char, struct std::char_traits<char>, class std::allocator<char>><class std::basic_string_view<char, struct std::char_traits<char>>, 0>(class std::basic_string_view<char, struct std::char_traits<char>> const &, class std::allocator<char> const &)
==21384==ABORTING

C:\Users\marek r\Downloads>cl /std:c++20 /EHcs bug.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.38.33133 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

bug.cpp
Microsoft (R) Incremental Linker Version 14.38.33133.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:bug.exe
bug.obj

C:\Users\marek r\Downloads>bug.exe

CRASH

问题分析与解决方案 #

问题本质 #

这段代码符合C++标准，崩溃是MSVC的已知Bug：在处理constexpr std::initializer_list<std::string_view>数组时，空初始化列表的元素会被错误地初始化，导致后续遍历访问时出现空指针引用。

保留constexpr的修复方案 #

以下方案可在保留constexpr测试数据的前提下解决问题：

1. 替换容器类型：用std::array<std::vector<std::string_view>, N>代替initializer_list数组。std::vector在C++20支持constexpr初始化，MSVC对其处理更可靠：

   #include <array>
   // ...
   constexpr std::array<std::vector<std::string_view>, 3> data{
       std::vector<std::string_view>{},
       std::vector<std::string_view>{"aa"sv, "bb"sv},
       std::vector<std::string_view>{"cc"sv, "dd"sv, "ee"sv}
   };
   

2. 避免空initializer_list：如果逻辑允许，将空的初始化列表替换为包含一个空string_view的列表，后续遍历可跳过空元素；若必须保留空列表，可显式初始化空initializer_list（部分版本MSVC可能仍存在问题，推荐方案1）。

3. 升级MSVC版本：该Bug在MSVC的后续版本中已被修复，升级编译器到较新版本可直接解决问题。

内容的提问来源于stack exchange，提问作者Marek R