Create a string with delimeters from fold expression

Question

I've got the following function:

template<typename... Args>
void Foo(Args && ... args)
{
    std::stringstream stream;
    (stream << ... << args);
    // Do somethign with it
}

It can perfectly concat params into a string, but as expected it gives the output without any delimiter. Is it possible to somehow delimit the inputs from each other?

Sample output:

elg.Debug("asd", "qwe", 123);

// Prints: asdqwe123

// Should prints something LIKE: asd qwe 123

Do I have to roll my own stringstream replacement for this?

If you want "output" with a specific separator, then perhaps using [`std::ostream_iterator`](https://en.cppreference.com/w/cpp/iterator/ostream_iterator) would be better? — Some programmer dude, Apr 10 '19 at 05:57

Yashas · Accepted Answer · 2021-06-26T06:42:41.067

15

With trailing delimiter:

template<typename... Args>
void debug(Args&& ... args)
{   
    std::ostringstream stream;
    ((stream << args << ' '), ...);
}

Without trailing delimiter:

template<typename FirstArg, typename... Args>
void debug(FirstArg&& firstArg, Args&& ... args)
{   
    std::ostringstream stream;
    stream << firstArg;
    ((stream << ", " << args), ...);
}

If the race is to have the shortest code, then last two lines can be merged into one: stream << firstArg, ((stream << ", " << args), ...);.

#include <iostream>

template<typename... Args>
void debug(Args&& ... args)
{   
    ((std::cout << args << ' '), ...);
}

int main () {
    debug("asd", 112, 0.04);
    return 0;   
}

Output: asd 112 0.04

edited Jun 26 '21 at 06:42

answered Apr 10 '19 at 06:31

Yashas

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Wow, even though, this is marked as duplicate, I couldn't see anything near this useful answer around SO. Thanks, it just works perfectly! – original.roland Apr 10 '19 at 16:13
1

I has small problem, `((stream << args << ','), ...)` has trailing comma at the end. – Phạm Văn Thông Jul 10 '19 at 15:02
I did not understand. I think the comma at the end is correct. Ref: https://en.cppreference.com/w/cpp/language/fold – Yashas Jul 10 '19 at 15:34
Comma at the end is correct behavior of fold expression but not definitely what the user needs. – Zheng Qu Jun 24 '21 at 19:05
@ZhengQu Silly me. Thanks. – Yashas Jun 26 '21 at 06:37

Create a string with delimeters from fold expression

1 Answers1