核心：
auto helper = [](std::filebuf& fb) -> int {
class Helper : public std::filebuf {
public:
int handle() { return _M_file.fd(); }
};
return static_cast<Helper&>(fb).handle();
};
示例：
#include <iostream>
#include <fstream>
#include <string>
#include <unistd.h>
int main()
{
std::string str("Hello World");
std::ofstream fs("path",
std::ofstream::binary | std::ofstream::out | std::ofstream::in);
if (!fs.is_open())
fs.open("path",
std::ofstream::binary | std::ofstream::out);
auto helper = [](std::filebuf& fb) -> int {
class Helper : public std::filebuf {
public:
int handle() { return _M_file.fd(); }
};
return static_cast<Helper&>(fb).handle();
};
int fd = helper(*fs.rdbuf());
fs.seekp(0, fs.beg);
fs.write(str.data(), str.length());
fsync(fd);
fs.close();
return 0;
}
