Piping between Functions

[christopher diggins]

I just wanted to share this technique for piping the cout from one function
to the cin of another, using the pipe operator:

#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);
}

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;
}

Any comments or suggestions?

I am working on a version which allows passing of arguments to functions,
and which allows arbitrary chaining.

 

[Alex Vinokur]

I just wanted to share this technique for piping the cout from one function
to the cin of another, using the pipe operator:

#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);
}

void HelloWorld() {
cout << "hello world" << endl;
}

void CountChars() {
string s; --------------------------------
s = cin.getline();

// Compiler g++ 3.3.3
In function `void CountChars()':
error: no matching function for call to `std::basic_istream<char,
std::char_traits<char> >::getline()'
/usr/include/c++/3.3.3/bits/istream.tcc:594: error: candidates are:
std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT,
_Traits>::getline(_CharT*, int, _CharT) [with _CharT = char, _Traits =
std::char_traits<char>]
/usr/include/c++/3.3.3/istream:401: error:
std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT,
_Traits>::getline(_CharT*, int) [with _CharT = char, _Traits =

cout << static_cast<int>(s.size()) << endl;
}

int main() {
filter(HelloWorld) | filter(CountChars);
return 0;
}

Any comments or suggestions?

I am working on a version which allows passing of arguments to functions,
and which allows arbitrary chaining.

[snip]

 

[christopher diggins]

Thanks for pointing that out Alex. My apologies for the error. Please
update:

void CountChars() {
string s;
s = cin.getline();
cout << static_cast<int>(s.size()) << endl;
}

to

void CountChars() {
string s;
getline(cin, s);
cout << static_cast<int>(s.size()) << endl;
}

 

[Alex Vinokur]

Thanks for pointing that out Alex. My apologies for the error. Please
update:

void CountChars() {
string s;
s = cin.getline();
cout << static_cast<int>(s.size()) << endl;
}

to

void CountChars() {
string s;
getline(cin, s);
cout << static_cast<int>(s.size()) << endl;
}

[snip]

Piping between functions looks very nice.

How do you mean to use that?

Are there any list of samples/applications?

 

[christopher diggins]

Thanks for pointing that out Alex. My apologies for the error. Please
update:

void CountChars() {
string s;
s = cin.getline();
cout << static_cast<int>(s.size()) << endl;
}

to

void CountChars() {
string s;
getline(cin, s);
cout << static_cast<int>(s.size()) << endl;
}

[snip]

Piping between functions looks very nice.

How do you mean to use that?

Are there any list of samples/applications?

I am using the techniuq to develop my applications in a more reusable
manner. For instance I can write many of my applications (currently
primarily text parsing tools) as filters. I can then string them together to
create new functions/applications. My plan is to code C++ as if I was
writing unix shell scripts. It basically reduces the amount of code I need
for my applications, which I always like.