C++ cout auto separator - c++

Question

I am wondering if there is way that std::cout automatically will insert some predefined value between printed sequences.
For example:
std::cout << 2 << 3 << 33 << 45 << std::endl;
outputs
233345
and I would like it to output
2 3 33 45
and I know, that it's easy to:
std::cout << 2 << " " << 3 << " " << 33 << " " << 45 << std::endl;
But I'am wondering if there is a way to automate this, such as:
std::cout << set_some_separator(" ") << 2 << 3 << 33 << 45 << std::endl;
Anyone aware of something like this being possible?

Answer 1

Well, I got beaten to it. I'll post this anyway.
Edit : well, after reading Nim's answer, mine does achieve the exact syntax OP wished for.
#include <iostream>
#include <algorithm>
struct with_separator {
with_separator(std::string sep)
: sep(std::move(sep)) {}
std::string sep;
};
struct separated_stream {
separated_stream(std::ostream &stream, std::string sep)
: _stream(stream), _sep(std::move(sep)), _first(true) {}
template <class Rhs>
separated_stream &operator << (Rhs &&rhs) {
if(_first)
_first = false;
else
_stream << _sep;
_stream << std::forward<Rhs>(rhs);
return *this;
}
separated_stream &operator << (std::ostream &(*manip)(std::ostream&)) {
manip(_stream);
return *this;
}
private:
std::ostream &_stream;
std::string _sep;
bool _first;
};
separated_stream operator << (std::ostream &stream, with_separator wsep) {
return separated_stream(stream, std::move(wsep.sep));
}
int main()
{
std::cout << with_separator(", ") << 1 << 2 << 3 << std::endl;
}
Output :
1, 2, 3

Answer 2

Simple answer is No, however, you can roll your own...
#include <iostream>
#include <sstream>
using namespace std;
struct set_some_separator{
set_some_separator(const char* sep) : _sep(sep)
{ };
template <typename T>
set_some_separator& operator<<(const T& v)
{
_str << v << _sep;
return *this;
}
friend
ostream& operator<<(ostream& os, const set_some_separator& s)
{ return os << s._str.str(); }
const char* _sep;
ostringstream _str;
};
int main()
{
cout << (set_some_separator(" ") << 2 << 3 << 33 << 45) << endl;
}
Okay the format of the cout is slightly different, hey-ho...

Answer 3

Not quite the same thing, but:
#include <array>
#include <iostream>
#include <iterator>
int main() {
std::array<int, 3> data = { 1, 2, 3 };
std::ostream_iterator<int> out(std::cout, " ");
std::copy(data.begin(), data.end(), out);
std::cout << '\n';
return 0;
}

Answer 4

How about using the ostream_iterator
int main()
{
std::vector<int> data {2,3,33,45};
std::copy(std::begin(data), std::end(data),
std::ostream_iterator(std::cout, " "));
std::cout << "\n";
}

Answer 5

A C++17 fold expression with the comma operator can create a nice one-liner:
[](auto &&...xs){ ((std::cout << xs << ',') , ...); }(2,3,33,45);

Answer 6

Simple solution, maybe you can tweak it to use <<
template<typename T>
void myout(T value)
{
std::cout << value << std::endl;
}
template<typename First, typename ... Rest>
void myout(First first, Rest ... rest)
{
std::cout << first << " ";
myout(rest...);
}
myout('a',"Hello",1,2,3,22/7.0);

Answer 7

If you're just looking for a way to print a vector with its elements properly delimited (and without an extra delimiter at the end), try this:
#include <iostream>
#include <vector>
int main()
{
std::vector<int> v{1, 2, 3};
auto it = v.begin();
if (it != v.end())
{
std::cout << *it;
++it;
}
for (; it != v.end(); ++it)
{
std::cout << ", " << *it;
}
}