On Sat, 08 Jan 2005 14:24:51 -0500, christopher diggins <cdiggins@videotron.ca> wrote:
Thank you very much to everyone who has been helping me out, and have made some suggestions. It took me a bit to realize the implications of what some people were suggesting, so I apologize if I am a bit slow to catch up.
I now have code which allows two arbitrary functions ( which have no parameters and return void ) to be chained together from cout of one to the cin of the other:
void HelloWorld() { cout << "hello world" << endl; }
void CountChars() { string s; s = cin.getline(); cout << static_cast<int>(s.size()) << endl; }
int main() { filter(HelloWorld) | filter(CountChars); return 0; }
This is done by redirecting cout for the first function to a temporary stringstream buffer, and then redirecting the output of the second stream. The code to accomplish this is trivial, but potentially interesting for the community:
#include <iostream> #include <sstream>
using namespace std;
typedef void(*procedure)();
class filter { public: filter(procedure x) : proc(x) { } void operator()(istream& in, ostream& out) { streambuf* inbuf = cin.rdbuf(); streambuf* outbuf = cout.rdbuf(); cin.rdbuf(in.rdbuf()); cout.rdbuf(out.rdbuf()); proc(); cin.rdbuf(inbuf); cout.rdbuf(outbuf); } private: procedure proc; };
void operator|(filter f1, filter f2) { stringstream s; f1(cin, s); s.seekg(0); f2(s, cout); }
Many good suggestions have been made so far. Some possibilities for more features are:
1) create wrapper objects around the filters, this would allow the passing of data to functions, like a command line string 2) chain arbitrarily long sequences by creating a pipeline object, and doing the piping in its destructor 3) allow the chaining of streams 4) allow the chaining of the various iostreams concepts 5) allow the chaining of FILE* (i.e. popen, etc.) 6) allow the chaining of processes 7) allow threading of functions
Any comments or suggestions? Is this a direction people would like to see continued? Also is anyone interested in collaborating?
Allow the two functions to be run as coroutines, and you'll have something really interesting. --Matt