popen_streambuf

#include <cstdio>
#include <iostream>
#include <fstream>

#define BUFFER_SIZE 1024

class popen_streambuf : public std::streambuf {
public:
	popen_streambuf()
	: _fp(NULL)
	, _buffer(NULL) {
	}
	~popen_streambuf() {
		close();
		if (_buffer != NULL)
			delete [] _buffer;
	}
	popen_streambuf* open(const char *command, const char *mode) {
		close();
		_fp = popen(command, mode);
		if (_fp == NULL)
			return NULL;
		_buffer = new char_type[BUFFER_SIZE];
		if (_buffer == NULL) {
			close();
			return NULL;
		}
		setg(_buffer, _buffer, _buffer);
		return this;
	}
	void close() {
		if (_fp != NULL) {
			pclose(_fp);
			_fp = NULL;
		}
	}
	std::streamsize xsgetn(char_type *ptr, std::streamsize n) {
		std::streamsize got = showmanyc();
		if (n <= got) {
			memcpy(ptr, gptr(), n * sizeof(char_type));
			gbump(n);
			return n;
		}
		memcpy(ptr, gptr(), got * sizeof(char_type));
		gbump(got);
		if (traits_type::eof() == underflow()) {
			return got;
		}
		return (got + xsgetn(ptr + got, n - got));
	}
	int_type underflow() {
		if (gptr() == 0)
			return traits_type::eof();
		if (gptr() < egptr())
			return traits_type::to_int_type(*gptr());
		size_t len = fread(eback(), sizeof(char_type), BUFFER_SIZE, _fp);
		setg(eback(), eback(), eback() + (sizeof(char_type) * len));
		if (0 == len)
			return traits_type::eof();
		return traits_type::to_int_type(*gptr());
	}
	std::streamsize showmanyc() {
		if (gptr() == 0) {
			return 0;
		}
		if (gptr() < egptr()) {
			return egptr() - gptr();
		}
		return 0;
	}
private:
	FILE *_fp;
	char_type *_buffer;
};

int main(int argc, char *argv) {
	std::ofstream output;
	output.open("bla.txt");
	popen_streambuf popen_buf;
	if (popen_buf.open("ps auxww", "r") == NULL) {
		std::cerr << "Error..." << std::endl;
		return 1;
	}
	output << &popen_buf;

// Use the aline above, or:
// 	char buffer[256];
// 	std::istream input(&popen_buf);
// 	while (input.read(buffer, 256)) {
// 		output << buffer;
// 	}

	output.close();

    return 0;
}