Question

我无法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(1)和(2)这两个实例中，我更期待

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

成功。

我在这里真正想念的是什么？感谢。

Answer 1

你这样做是错误的。您要将streambuf从istringstream分配到filestream，您应该从另一个方向进行分配。即：

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.

Boost.IOStreams：如何使用'rdbuf'正确重定向文件流？

1 个答案: