#include <streambuf>#include <ostream>#include <functional>#include <string>#include <memory>#include <iostream> // only for testing...#if HAS_FUNCTIONtypedef std::function<voID(std::string)> function_type;#elseclass function_type{private: struct base { virtual ~base() {} virtual base* clone() const = 0; virtual voID call(std::string const&) = 0; }; template <typename Function> struct concrete : base { Function d_function; concrete(Function function) : d_function(function) { } base* clone() const { return new concrete<Function>(this->d_function); } voID call(std::string const& value) { this->d_function(value); } }; std::auto_ptr<base> d_function;public: template <typename Function> function_type(Function function) : d_function(new concrete<Function>(function)) { } function_type(function_type const& other) : d_function(other.d_function->clone()) { } function_type& operator= (function_type other) { this->swap(other); return *this; } ~function_type() {} voID swap(function_type& other) { std::swap(this->d_function,other.d_function); } voID operator()(std::string const& value) { this->d_function->call(value); }};#endifclass functionbuf : public std::streambuf {private: typedef std::streambuf::traits_type traits_type; function_type d_function; char d_buffer[1024]; int overflow(int c) { if (!traits_type::eq_int_type(c,traits_type::eof())) { *this->pptr() = traits_type::to_char_type(c); this->pbump(1); } return this->sync()? traits_type::not_eof(c): traits_type::eof(); } int sync() { if (this->pbase() != this->pptr()) { this->d_function(std::string(this->pbase(),this->pptr())); this->setp(this->pbase(),this->epptr()); } return 0; }public: functionbuf(function_type const& function) : d_function(function) { this->setp(this->d_buffer,this->d_buffer + sizeof(this->d_buffer) - 1); }};class ofunctionstream : private virtual functionbuf,public std::ostream {public: ofunctionstream(function_type const& function) : functionbuf(function),std::ostream(static_cast<std::streambuf*>(this)) { this->flags(std::ios_base::unitbuf); }};voID some_function(std::string const& value) { std::cout << "some_function(" << value << ")\n";}int main() { ofunctionstream out(&some_function); out << "hello" << ',' << " world: " << 42 << "\n"; out << std::nounitbuf << "not" << " as " << "many" << " calls\n" << std::flush;}
上面代码的一大部分实际上与手头的任务无关:它实现了std :: function< voID(std :: string)>的原始版本.如果C 2011无法使用.
如果你不想要那么多的调用,你可以关闭std :: ios_base :: unitbuf并仅在刷新流时发送数据,例如使用std :: flush(是的,我知道std :: endl但不幸的是它通常被误用,我强烈建议摆脱它并使用std :: flush,其中一个flush是真的意思).
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