如果你想在stdlib内部纯粹完成这个任务,那么你的设计是正确的。
有一件事情:不要在每次输出时都向每个streambuf进行tee操作,而是实现它使用与其给定的一个streambuf相同的放置区域,并在溢出和同步时将其复制到其他streambuf中。这将最小化虚拟调用,这是streambuf工作方式的目标之一。
或者,如果你只想处理stdout和stderr(这很常见),可以通过标准Unix tee程序(或平台上的等效程序)运行程序,通过在调用程序时自己执行或在程序内部进行分叉,设置适当的流等来完成。
编辑: 你让我开始思考,我应该知道如何做对。这是我的第一个近似值。(当它坏掉时,你需要保留两个部分。)
#ifndef INCLUDE_GUARD_A629F54A136C49C9938CB33EF8EDE676
#define INCLUDE_GUARD_A629F54A136C49C9938CB33EF8EDE676
#include <cassert>
#include <cstring>
#include <streambuf>
#include <map>
#include <vector>
template<class CharT, class Traits=std::char_traits<CharT> >
struct basic_streamtee : std::basic_streambuf<CharT, Traits> {
typedef std::basic_ios<CharT, Traits> Stream;
typedef std::basic_streambuf<CharT, Traits> StreamBuf;
typedef typename StreamBuf::char_type char_type;
typedef typename StreamBuf::traits_type traits_type;
typedef typename StreamBuf::int_type int_type;
typedef typename StreamBuf::pos_type pos_type;
typedef typename StreamBuf::off_type off_type;
basic_streamtee() : _key_buf(0) {}
basic_streamtee(Stream& a, Stream& b) : _key_buf(0) {
this->pubimbue(a.rdbuf()->getloc());
_set_key_buf(a.rdbuf());
insert(a);
insert(b);
}
~basic_streamtee() {
sync();
for (typename std::map<Stream*, StreamBuf*>::iterator i = _bufs.begin();
i != _bufs.end();
++i)
{
StreamBuf* old = i->first->rdbuf(i->second);
if (old != this) {
old->pubsync();
}
}
}
void insert(Stream& s) {
sync();
if (!_bufs.count(&s)) {
if (!_key_buf) {
_set_key_buf(s.rdbuf());
}
_bufs[&s] = s.rdbuf(this);
}
}
void remove(Stream& s) {
sync();
typename std::map<Stream*, StreamBuf*>::iterator i = _bufs.find(&s);
if (i != _bufs.end()) {
StreamBuf* old = i->second;
i->first->rdbuf(i->second);
_bufs.erase(i);
if (old == _key_buf) {
_set_key_buf(_bufs.empty() ? 0 : _bufs.begin()->second);
}
}
}
private:
basic_streamtee(basic_streamtee const&);
basic_streamtee& operator=(basic_streamtee const&);
StreamBuf* _key_buf;
std::map<Stream*, StreamBuf*> _bufs;
void _set_key_buf(StreamBuf* p) {
_key_buf = p;
_update_put_area();
}
void _update_put_area() {
if (!_key_buf) {
this->setp(0, 0);
}
else {
this->setp((_key_buf->*&basic_streamtee::pbase)(),
(_key_buf->*&basic_streamtee::epptr)());
}
}
#define FOREACH_BUF(var) \
for (typename std::map<Stream*, StreamBuf*>::iterator var = _bufs.begin(); \
var != _bufs.end(); ++var)
virtual void imbue(std::locale const& loc) {
FOREACH_BUF(iter) {
iter->second->pubimbue(loc);
}
}
virtual int sync() {
if (!_key_buf) {
return -1;
}
char_type* data = this->pbase();
std::streamsize n = this->pptr() - data;
(_key_buf->*&basic_streamtee::pbump)(n);
FOREACH_BUF(iter) {
StreamBuf* buf = iter->second;
if (buf != _key_buf) {
buf->sputn(data, n);
buf->pubsync();
}
}
_key_buf->pubsync();
_update_put_area();
return 0;
}
virtual std::streamsize xsputn(char_type const* s, std::streamsize n) {
assert(n >= 0);
if (!_key_buf) {
return 0;
}
if (this->epptr() - this->pptr() < n) {
sync();
}
if (this->epptr() - this->pptr() >= n) {
std::memcpy(this->pptr(), s, n);
this->pbump(n);
}
else {
FOREACH_BUF(iter) {
iter->second->sputn(s, n);
}
_update_put_area();
}
return n;
}
virtual int_type overflow(int_type c) {
bool const c_is_eof = traits_type::eq_int_type(c, traits_type::eof());
int_type const success = c_is_eof ? traits_type::not_eof(c) : c;
sync();
if (!c_is_eof) {
char_type cc = traits_type::to_char_type(c);
xsputn(&cc, 1);
}
return success;
}
#undef FOREACH_BUF
};
typedef basic_streamtee<char> streamtee;
typedef basic_streamtee<wchar_t> wstreamtee;
#endif
现在,这个测试还远没有完成,但似乎可以运行:
#include "streamtee.hpp"
#include <cassert>
#include <iostream>
#include <sstream>
int main() {
using namespace std;
{
ostringstream a, b;
streamtee tee(a, b);
a << 42;
assert(a.str() == "42");
assert(b.str() == "42");
}
{
ostringstream a, b;
streamtee tee(cout, a);
tee.insert(b);
a << 42 << '\n';
assert(a.str() == "42\n");
assert(b.str() == "42\n");
}
return 0;
}
将其与文件一起使用:
#include "streamtee.hpp"
#include <iostream>
#include <fstream>
struct FileTee {
FileTee(std::ostream& stream, char const* filename)
: file(filename), buf(file, stream)
{}
std::ofstream file;
streamtee buf;
};
int main() {
using namespace std;
FileTee out(cout, "stdout.txt");
FileTee err(clog, "stderr.txt");
streambuf* old_cerr = cerr.rdbuf(&err.buf);
cout << "stdout\n";
clog << "stderr\n";
cerr.rdbuf(old_cerr);
return 0;
}