使用 boost 将 C *FILE 转换为 C++ iostream

Question

我是 C++ 的新手，想将 *FILE（例如 popen() 返回的）转换为 iostream 以与 getline 等函数一起使用。我找到了以下代码 http://fw-geekycoder.blogspot.co.za/2011/06/how-to-convert-c-file-to-c-iostream.html ，以及来自很多地方的类似代码，但编译器抱怨 boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_sink> bis(fd); 和 boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_sink> bis(fd);

#include <iostream>
#include <cstdio>
#include <unistd.h>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>

void write() {
    FILE* fp = fopen("whatever.txt", "w");
    if (fp == NULL) {
        perror("fopen error");
    }
    int fd = fileno(fp);
    boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_sink> bis(fd);
    std::ostream os(&bis);
    os << "Hello World!" << std::endl;

    fclose(fp);
}

void read() {
    FILE* fp = fopen("whatever.txt", "r");
    if (fp == NULL) {
        perror("fopen error");
    }
    int fd = fileno(fp);
    boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_source> bis(fd);
    std::istream is(&bis);
    while (is) {
        std::string line;
        std::getline(is, line);
        std::cout << line << std::endl;
    }
    fclose(fp);
}

int main() {
    write();
    read();

    return 0;
}

我的系统似乎得到了提升，但好像 API 或其他东西发生了变化。有什么问题，这是我在 eclipse 中的输出：

make all 
Building file: ../src/boostPopenHandler.cpp
Invoking: GCC C++ Compiler
g++ -D__GXX_EXPERIMENTAL_CXX0X__ -I../../emdw/src -I../../patrecII/src -I../../ -O0 -g3 -Wall -c -fmessage-length=0 -std=c++0x -MMD -MP -MF"src/boostPopenHandler.d" -MT"src/boostPopenHandler.d" -o"src/boostPopenHandler.o" "../src/boostPopenHandler.cpp"
In file included from ../src/boostPopenHandler.cpp:4:0:
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = char; std::ios_base::openmode = std::_Ios_Openmode]’:
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = char; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:13:83:   required from here
/usr/include/boost/iostreams/device/file_descriptor.hpp:276:36: error: invalid conversion from ‘char’ to ‘const char*’ [-fpermissive]
     { open(detail::path(path), mode); }
                                    ^
In file included from /usr/include/boost/iostreams/device/file_descriptor.hpp:26:0,
                 from ../src/boostPopenHandler.cpp:4:
/usr/include/boost/iostreams/detail/path.hpp:52:5: error:   initializing argument 1 of ‘boost::iostreams::detail::path::path(const char*)’ [-fpermissive]
     path(const char* p) : narrow_(p), wide_(), is_wide_(false) { }
     ^
In file included from ../src/boostPopenHandler.cpp:4:0:
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_source::file_descriptor_source(const Path&, std::ios_base::openmode) [with Path = char; std::ios_base::openmode = std::_Ios_Openmode]’:
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = char; T = boost::iostreams::file_descriptor_source; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::input_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:26:85:   required from here
/usr/include/boost/iostreams/device/file_descriptor.hpp:194:36: error: invalid conversion from ‘char’ to ‘const char*’ [-fpermissive]
     { open(detail::path(path), mode); }
                                    ^
In file included from /usr/include/boost/iostreams/device/file_descriptor.hpp:26:0,
                 from ../src/boostPopenHandler.cpp:4:
/usr/include/boost/iostreams/detail/path.hpp:52:5: error:   initializing argument 1 of ‘boost::iostreams::detail::path::path(const char*)’ [-fpermissive]
     path(const char* p) : narrow_(p), wide_(), is_wide_(false) { }
     ^
make: *** [src/boostPopenHandler.o] Error 1

编辑:
根据Selçuk Cihan的回答，我将相关代码修改为：

boost::iostreams::file_descriptor_source fds(fd);
boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_sink> 
...
boost::iostreams::file_descriptor_source fds(fd);
boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_source>

但我仍然得到编译错误列表：

**** Build of configuration Debug for project boostPopenHandler ****

make all 
Building file: ../src/boostPopenHandler.cpp
Invoking: GCC C++ Compiler
g++ -I../../emdw/src -I../../patrecII/src -I../../ -O0 -g3 -Wall -c -fmessage-length=0 -std=c++0x -MMD -MP -MF"src/boostPopenHandler.d" -MT"src/boostPopenHandler.d" -o"src/boostPopenHandler.o" "../src/boostPopenHandler.cpp"
In file included from ../src/boostPopenHandler.cpp:4:0:
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_source::file_descriptor_source(const Path&, std::ios_base::openmode) [with Path = int; std::ios_base::openmode = std::_Ios_Openmode]’:
../src/boostPopenHandler.cpp:13:52:   required from here
/usr/include/boost/iostreams/device/file_descriptor.hpp:194:36: error: invalid conversion from ‘int’ to ‘const char*’ [-fpermissive]
     { open(detail::path(path), mode); }
                                    ^
In file included from /usr/include/boost/iostreams/device/file_descriptor.hpp:26:0,
                 from ../src/boostPopenHandler.cpp:4:
/usr/include/boost/iostreams/detail/path.hpp:52:5: error:   initializing argument 1 of ‘boost::iostreams::detail::path::path(const char*)’ [-fpermissive]
     path(const char* p) : narrow_(p), wide_(), is_wide_(false) { }
     ^
In file included from ../src/boostPopenHandler.cpp:4:0:
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = boost::iostreams::file_descriptor_source; std::ios_base::openmode = std::_Ios_Openmode]’:
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = boost::iostreams::file_descriptor_source; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:14:84:   required from here
/usr/include/boost/iostreams/device/file_descriptor.hpp:276:36: error: no matching function for call to ‘boost::iostreams::detail::path::path(const boost::iostreams::file_descriptor_source&)’
     { open(detail::path(path), mode); }
                                    ^
/usr/include/boost/iostreams/device/file_descriptor.hpp:276:36: note: candidates are:
In file included from /usr/include/boost/iostreams/device/file_descriptor.hpp:26:0,
                 from ../src/boostPopenHandler.cpp:4:
/usr/include/boost/iostreams/detail/path.hpp:138:5: note: boost::iostreams::detail::path::path(const wstring&)
     path(const std::wstring&);
     ^
/usr/include/boost/iostreams/detail/path.hpp:138:5: note:   no known conversion for argument 1 from ‘const boost::iostreams::file_descriptor_source’ to ‘const wstring& {aka const std::basic_string<wchar_t>&}’
/usr/include/boost/iostreams/detail/path.hpp:70:5: note: boost::iostreams::detail::path::path(const boost::iostreams::detail::path&)
     path(const path& p) 
     ^
/usr/include/boost/iostreams/detail/path.hpp:70:5: note:   no known conversion for argument 1 from ‘const boost::iostreams::file_descriptor_source’ to ‘const boost::iostreams::detail::path&’
/usr/include/boost/iostreams/detail/path.hpp:64:14: note: template<class Path> boost::iostreams::detail::path::path(const Path&, typename Path::codecvt_type*)
     explicit path(const Path& p, typename Path::codecvt_type* = 0)
              ^
/usr/include/boost/iostreams/detail/path.hpp:64:14: note:   template argument deduction/substitution failed:
/usr/include/boost/iostreams/detail/path.hpp: In substitution of ‘template<class Path> boost::iostreams::detail::path::path(const Path&, typename Path::codecvt_type*) [with Path = boost::iostreams::file_descriptor_source]’:
/usr/include/boost/iostreams/device/file_descriptor.hpp:276:36:   required from ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = boost::iostreams::file_descriptor_source; std::ios_base::openmode = std::_Ios_Openmode]’
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = boost::iostreams::file_descriptor_source; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:14:84:   required from here
/usr/include/boost/iostreams/detail/path.hpp:64:14: error: no type named ‘codecvt_type’ in ‘class boost::iostreams::file_descriptor_source’
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = boost::iostreams::file_descriptor_source; std::ios_base::openmode = std::_Ios_Openmode]’:
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = boost::iostreams::file_descriptor_source; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:14:84:   required from here
/usr/include/boost/iostreams/detail/path.hpp:57:14: note: template<class Path> boost::iostreams::detail::path::path(const Path&, typename Path::external_string_type*)
     explicit path(const Path& p, typename Path::external_string_type* = 0)
              ^
/usr/include/boost/iostreams/detail/path.hpp:57:14: note:   template argument deduction/substitution failed:
/usr/include/boost/iostreams/detail/path.hpp: In substitution of ‘template<class Path> boost::iostreams::detail::path::path(const Path&, typename Path::external_string_type*) [with Path = boost::iostreams::file_descriptor_source]’:
/usr/include/boost/iostreams/device/file_descriptor.hpp:276:36:   required from ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = boost::iostreams::file_descriptor_source; std::ios_base::openmode = std::_Ios_Openmode]’
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = boost::iostreams::file_descriptor_source; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:14:84:   required from here
/usr/include/boost/iostreams/detail/path.hpp:57:14: error: no type named ‘external_string_type’ in ‘class boost::iostreams::file_descriptor_source’
/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_sink::file_descriptor_sink(const Path&, std::ios_base::openmode) [with Path = boost::iostreams::file_descriptor_source; std::ios_base::openmode = std::_Ios_Openmode]’:
/usr/include/boost/iostreams/stream_buffer.hpp:94:5:   required from ‘boost::iostreams::stream_buffer<T, Tr, Alloc, Mode>::stream_buffer(U100&, typename boost::disable_if<boost::is_same<U0, T> >::type*) [with U100 = boost::iostreams::file_descriptor_source; T = boost::iostreams::file_descriptor_sink; Tr = std::char_traits<char>; Alloc = std::allocator<char>; Mode = boost::iostreams::output_seekable; typename boost::disable_if<boost::is_same<U0, T> >::type = void]’
../src/boostPopenHandler.cpp:14:84:   required from here
/usr/include/boost/iostreams/detail/path.hpp:52:5: note: boost::iostreams::detail::path::path(const char*)
     path(const char* p) : narrow_(p), wide_(), is_wide_(false) { }
     ^
/usr/include/boost/iostreams/detail/path.hpp:52:5: note:   no known conversion for argument 1 from ‘const boost::iostreams::file_descriptor_source’ to ‘const char*’
/usr/include/boost/iostreams/detail/path.hpp:49:5: note: boost::iostreams::detail::path::path(const string&)
     path(const std::string& p) : narrow_(p), wide_(), is_wide_(false) { }
     ^
/usr/include/boost/iostreams/detail/path.hpp:49:5: note:   no known conversion for argument 1 from ‘const boost::iostreams::file_descriptor_source’ to ‘const string& {aka const std::basic_string<char>&}’
/usr/include/boost/iostreams/detail/path.hpp:46:5: note: boost::iostreams::detail::path::path()
     path() : narrow_(), wide_(), is_wide_(false) { }
     ^
/usr/include/boost/iostreams/detail/path.hpp:46:5: note:   candidate expects 0 arguments, 1 provided
make: *** [src/boostPopenHandler.o] Error 1

Answer 1

哦，你应该先声明一个file_descriptor_source，如

boost::iostreams::file_descriptor_source fds(fd);

然后是您的流缓冲区

boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_source> bis(fds);

编辑：

很抱歉造成混淆，不推荐使用带有 int 参数的 ctor，而且您似乎没有那个 ctor，否则您的代码将完美编译。这就是为什么我提供的上述代码需要 boost::iostreams::never_close_handle 或 boost::iostreams::close_handle

的第二个强制参数

所以它应该是

boost::iostreams::file_descriptor_source fds(fd, boost::iostreams::close_handle);

否则你仍然会得到那个错误。同样的修复也适用于 file_descriptor_sink。

现在你应该如何阅读错误：

/usr/include/boost/iostreams/device/file_descriptor.hpp: In instantiation of ‘boost::iostreams::file_descriptor_source::file_descriptor_source(const Path&, std::ios_base::openmode) [with Path = char; std::ios_base::openmode = std::_Ios_Openmode]’:

说它试图用

的模板参数选项实例化一个 file_descriptor_source

[with Path = char; std::ios_base::openmode = std::_Ios_Openmode]

由于您只提供了一个整数，编译器试图匹配该版本的构造函数，但未能进行转换。

Answer 2

您不需要 Boost。

wanted to convert a *FILE (such as returned by popen()) to a iostream

改用pstreams（免责声明，我写的，如果重要的话）。

一些编译器提供扩展来从 C 文件创建 streambuf 而无需 Boost，例如使用 GCC：

#include <ext/stdio_filebuf.h>
...
__gnu_cxx::stdio_filebuf<char> fb(fp, std::ios::out);
std::ostream os(&fb);

使用 boost 将 C *FILE 转换为 C++ iostream

Convert C *FILE to C++ iostream with boost

c++

boost

iostream

boost-iostreams