为什么std :: size()在gcc 8.2.0中不是std的成员 [英] Why std::size() is not a member of std in gcc 8.2.0

问题描述

我正在尝试教自己一些C ++ 17.

I'm trying to teach myself some C++17.

为什么编译器会为以下代码片段引发错误?

Why is the compiler throwing an error for the below code snippet?

#include <iostream> 
#include <vector>
#include <iterator>

int main() 
{
    std::vector<int> v = { 3, 1, 4 };
    std::cout << std::size(v) << '\n'; 

    int a[] = { -5, 10, 15 };
    std::cout << std::size(a) << '\n';
}

编译器抛出以下错误

manish@Manish-Tummala:~/c_files$ g++ 6.cpp -o - 6.out
6.cpp: In function ‘int main()’:
6.cpp:8:23: error: ‘size’ is not a member of ‘std’
     std::cout << std::size(v) << '\n';
                       ^~~~
6.cpp:8:23: note: suggested alternative: ‘size_t’
     std::cout << std::size(v) << '\n';
                       ^~~~
                       size_t
6.cpp:11:23: error: ‘size’ is not a member of ‘std’
     std::cout << std::size(a) << '\n';
                       ^~~~
6.cpp:11:23: note: suggested alternative: ‘size_t’
     std::cout << std::size(a) << '\n';
                       ^~~~
                       size_t

推荐答案

有关GCC中的C ++ 17支持，请参考:

For C++17 support in GCC, please refer to:

• GCC中的C ++ 17支持

暂时，默认情况下未启用C ++ 17支持:

For the time being, C++17 support is not enabled by default:

要启用C ++ 17支持，请将命令行参数-std=c++17添加到您的g++命令行中.或者，要启用除C ++ 17功能之外的GNU扩展，请添加-std=gnu++17.

To enable C++17 support, add the command-line parameter -std=c++17 to your g++ command line. Or, to enable GNU extensions in addition to C++17 features, add -std=gnu++17.

目前，用于GCC的C ++ 17 ABI尚未完成.这意味着今天以C ++ 17模式构建的程序可能无法链接到同样以C ++ 17模式编译的过去或将来的二进制文件(或在运行时崩溃).稳定的ABI可确保跨编译器版本实现这种互操作性.

At present, the C++17 ABI for GCC has not been finalized yet. This means that programs built today in C++17 mode may not be able to link against past or future binaries also compiled in C++17 mode (or crash at run time). A stable ABI ensures such interoperability across compiler versions.

一旦ABI最终确定，GCC的未来版本将默认启用C ++ 17模式.

Once the ABI is final, a future version of GCC will enable C++17 mode by default.

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