istream eof libc ++和libstdc ++之间的差异 [英] istream eof discrepancy between libc++ and libstdc++

问题描述

以下（玩具）程序在链接到libstdc ++和libc ++时会返回不同的内容。这是libc ++中的一个错误，或者我不明白istream eof（）如何工作？我试过运行它使用g ++在linux和mac os x和clang在mac os x，有​​和没有-std = c ++ 0x。这是我的印象，eof（）不返回true，直到尝试读取（通过get（）或其他）实际上失败。这是libstdc ++的行为，但不是libc ++的行为。

The following (toy) program returns different things when linked against libstdc++ and libc++. Is this a bug in libc++ or do I not understand how istream eof() works? I have tried running it using g++ on linux and mac os x and clang on mac os x, with and without -std=c++0x. It was my impression that eof() does not return true until an attempt to read (by get() or something else) actually fails. This is how libstdc++ behaves, but not how libc++ behaves.

#include <iostream>
#include <sstream>

int main() {
    std::stringstream s;

    s << "a";

    std::cout << "EOF? " << (s.eof() ? "T" : "F") << std::endl;
    std::cout << "get: " << s.get() << std::endl;
    std::cout << "EOF? " << (s.eof() ? "T" : "F") << std::endl;

return 0;
}

Thor:~$ g++ test.cpp
Thor:~$ ./a.out
EOF? F
get: 97
EOF? F
Thor:~$ clang++ -std=c++0x -stdlib=libstdc++ test.cpp 
Thor:~$ ./a.out
EOF? F
get: 97
EOF? F
Thor:~$ clang++ -std=c++0x -stdlib=libc++ test.cpp 
Thor:~$ ./a.out
EOF? F
get: 97
EOF? T
Thor:~$ clang++ -stdlib=libc++ test.cpp 
Thor:~$ ./a.out
EOF? F
get: 97
EOF? T

推荐答案

这是一个libc ++错误， Cubbi指出。我的错。详情如下：

This was a libc++ bug and has been fixed as Cubbi noted. My bad. Details are here:

http://lwg.github.io/issues/lwg-closed.html#2036

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