使用 boost::filtering_streambuf 和 newline_filter 时的空文件
Empty file when using boost::filtering_streambuf with newline_filter
我希望将一段数据写入通过 std::fopen
使用 boost::iostreams::filtering_streambuf
和 newline_filter
打开的文件。
这是我一直在尝试使用的一个小型可重现测试用例。
它只是生成一个空文件。
#include <string>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <errno.h>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <iosfwd>
#include <string>
#include <boost/iostreams/flush.hpp>
#include <boost/iostreams/operations.hpp>
#include <fstream>
#include <cstdio>
int main()
{
FILE *fp = nullptr;
std::string d ("file");
fp = std::fopen(d.c_str(), "w");
const int fd = fileno(fp);
boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
boost::iostreams::filtering_streambuf<boost::iostreams::output>obuf;
#if defined(_WIN32)
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
#else
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::mac));
#endif
obuf.push(output);
std::ostream buffer(&obuf);
std::string myteststr = "Hello \n World\n";
buffer << myteststr;
buffer.flush();
boost::iostreams::flush(obuf);
return 0;
}
我在这里明显遗漏了什么吗?
我无法重现该行为:
这个是为了用
编译执行
g++ -std=c++14 -O2 -Wall -pedantic -pthread main.cpp -lboost_{system,iostreams} && ./a.out
file output.txt
xxd output.txt
版画
output.txt: ASCII text, with CRLF line terminators
00000000: 4865 6c6c 6f20 0d0a 2057 6f72 6c64 0d0a Hello .. World..
我确实建议添加明确的 fd
关闭,尽管这在技术上不重要。
此外,2019 年有没有理由使用 FILE*
?我假设您将其包括在内是因为遗留代码仅使用它。
¹ 清单:
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/flush.hpp>
#include <cstdio>
#include <iostream>
#include <string>
int main() {
FILE* fp = std::fopen("output.txt", "w");
const int fd = fileno(fp);
boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
boost::iostreams::filtering_streambuf<boost::iostreams::output> obuf;
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
obuf.push(output);
std::ostream buffer(&obuf);
std::string myteststr = "Hello \n World\n";
buffer << myteststr;
buffer.flush();
boost::iostreams::flush(obuf);
::close(fd);
}
我希望将一段数据写入通过 std::fopen
使用 boost::iostreams::filtering_streambuf
和 newline_filter
打开的文件。
这是我一直在尝试使用的一个小型可重现测试用例。
它只是生成一个空文件。
#include <string>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <errno.h>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <iosfwd>
#include <string>
#include <boost/iostreams/flush.hpp>
#include <boost/iostreams/operations.hpp>
#include <fstream>
#include <cstdio>
int main()
{
FILE *fp = nullptr;
std::string d ("file");
fp = std::fopen(d.c_str(), "w");
const int fd = fileno(fp);
boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
boost::iostreams::filtering_streambuf<boost::iostreams::output>obuf;
#if defined(_WIN32)
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
#else
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::mac));
#endif
obuf.push(output);
std::ostream buffer(&obuf);
std::string myteststr = "Hello \n World\n";
buffer << myteststr;
buffer.flush();
boost::iostreams::flush(obuf);
return 0;
}
我在这里明显遗漏了什么吗?
我无法重现该行为:
这个是为了用
编译执行g++ -std=c++14 -O2 -Wall -pedantic -pthread main.cpp -lboost_{system,iostreams} && ./a.out
file output.txt
xxd output.txt
版画
output.txt: ASCII text, with CRLF line terminators
00000000: 4865 6c6c 6f20 0d0a 2057 6f72 6c64 0d0a Hello .. World..
我确实建议添加明确的 fd
关闭,尽管这在技术上不重要。
此外,2019 年有没有理由使用 FILE*
?我假设您将其包括在内是因为遗留代码仅使用它。
¹ 清单:
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/filter/newline.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/flush.hpp>
#include <cstdio>
#include <iostream>
#include <string>
int main() {
FILE* fp = std::fopen("output.txt", "w");
const int fd = fileno(fp);
boost::iostreams::file_descriptor_sink output(fd, boost::iostreams::never_close_handle);
boost::iostreams::filtering_streambuf<boost::iostreams::output> obuf;
obuf.push(boost::iostreams::newline_filter(boost::iostreams::newline::dos));
obuf.push(output);
std::ostream buffer(&obuf);
std::string myteststr = "Hello \n World\n";
buffer << myteststr;
buffer.flush();
boost::iostreams::flush(obuf);
::close(fd);
}