'std :: basic_ostream< char>'中没有名为'str'的成员与gcc和clang，但与msvc没问题 [英] no member named 'str' in 'std::basic_ostream<char>' with gcc and clang, but no problem with msvc

问题描述

此代码段( https://gcc.godbolt.org/z/hKDMxm ):

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    auto s = (ostringstream{} << "string").str();
    cout << s;
    return 0; 
}

可使用msvc编译并按预期运行，但无法使用clang 9.0.0和gcc 9.2进行编译，并显示以下错误消息:在'std :: basic_ostream< char>'中没有名为'str'的成员.查看 https://en.cppreference.com/w/cpp/io/basic_ostringstream/str 显然是 ostringstream 的 str()成员.为什么clang和gcc无法编译此代码?

compiles and runs as expected with msvc, but fails to compile with clang 9.0.0 and gcc 9.2 giving this error message:no member named 'str' in 'std::basic_ostream<char>'. Looking at https://en.cppreference.com/w/cpp/io/basic_ostringstream/str there is clearly str() member of ostringstream. Why clang and gcc are failing to compile this code?

推荐答案

显然是 ostringstream

是的，但是根据 cppreference 这种<< 应该返回对 basic_ostream< ...> 的引用，而不是对 ostringstream 的引用.

Yes, but according to cppreference this overload of << should return a reference to basic_ostream<...> rather than ostringstream.

libstdc ++(GCC的标准库)完全做到了这一点，而libc ++(Clang的标准库)和MSVC的标准库在技术上在这里表现不正确.

libstdc++ (GCC's standard library) does exactly this, while libc++ (Clang's standard library) and MSVC's standard library behave incorrectly here, technically.

但是，似乎有一个打开的缺陷报告提示与右值流一起使用的<< 的重载应返回传递给它的确切流类型.如果它被接受，您的代码将是有效的.

However, it seems there is an open defect report suggesting that the overload of << that works with rvalue streams should return the exact stream type that was passed to it. If it gets accepted, your code will be valid.

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