Boost.IOStreams：如何用'rdbuf'正确地重定向文件流？

Question

我不可能找到以下行为的解释：

#include <boost/iostreams/device/file.hpp> 
#include <boost/iostreams/stream.hpp> 

#include <iostream> 
#include <sstream> 

TEST_CASE(rdbuf) { 
    { 
    boost::iostreams::stream<boost::iostreams::file_sink> file("test"); 

    file << "Hello, World!"; 
    } 
    { 
    boost::iostreams::stream<boost::iostreams::file_source> file("test"); 
    std::string            line; 

    std::getline(file, line); 
    CHECK_EQUAL(line, "Hello, World!"); 
    } 
    { 
    boost::iostreams::stream<boost::iostreams::file_source> file("test"); 
    std::istringstream          iss; 
    std::string            line; 

    file.rdbuf(iss.rdbuf()); 

    std::getline(file, line); 
    CHECK_EQUAL(line, ""); 

    std::getline(iss, line); 
    CHECK_EQUAL(line, ""); // (1) Why? 
    } 
    { 
    boost::iostreams::stream<boost::iostreams::file_source> file("test"); 
    std::ostringstream          oss; 
    std::string            line; 

    file.rdbuf(oss.rdbuf()); 

    std::getline(file, line); 
    CHECK_EQUAL(line, ""); 

    line = oss.str(); 
    CHECK_EQUAL(line, ""); // (2) Why? 
    } 
} 

在这两种情况下(1)和(2)，我本来打算

CHECK_EQUAL(line, "Hello, World!"); 

成功。

我在这里错过了什么？谢谢。

Answer 1

你这样做是错误的。你将streambuf从istringstream分配到filestream，你应该在另一个方向。 I.e .:

boost::iostreams::stream<boost::iostreams::file_source> file("test"); 
std::istringstream          iss; 
std::string            line; 

iss.rdbuf(file.rdbuf()); //assign the file to iss 

std::getline(file, line); 
CHECK_EQUAL(line, "Hello, World!"); 

std::getline(iss, line); 
CHECK_EQUAL(line, ""); // Empty, because the streambuf is shared.