C++ how to print words with views::split?

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In p0896r4

23.7.11.1 Overview [range.split.overview]

  1. split_view takes a View and a delimiter, and splits the View into subranges on the delimiter. The delimiter can be a single element or a View of elements.

Example (with slight modification to compile)

#include <iostream>
#include <ranges>
#include <string>
    
int main()
{
    std::string str{"the quick brown fox"};
    std::ranges::split_view sentence{str, ' '};
    for (auto word : sentence) {
        for (char ch : word)
            std::cout << ch;
        std::cout << "*";
    }
    return 0;
}

Outputs:

the*quick*brown*fox*

However this is printing char by char, why can't I print a word instead?

for (auto word : sentence) 
    std::cout << word << std::endl;

Error: https://godbolt.org/z/GsPrhz

<source>:10:19: error: no match for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'std::ranges::split_view<std::ranges::ref_view<std::__cxx11::basic_string<char> >, std::ranges::single_view<char> >::_OuterIter<true>::value_type')

Question: can I print the words? or does std::ranges::single_view<char> pose a contraint ?

c++20 c++
1 Answers

None of the standard views are printable, so the short answer is that you basically cannot. We're hoping to change this as part of P2214.

views::split specifically has the issue that you can't even get a contiguous subrange out of it, so you can't meaningfully convert the pieces you get into string_views either. This is P2210.

The best solution I can offer today is to use the fmt library, which lets you write:

char const* delim = "";
for (auto word : sentence) {
    fmt::print("{}{}", delim, fmt::join(word, ""));
    delim = " ";
}

I don't think fmt has any support for joining ranges of ranges, so I did the delimiting manually.

Note that single_view<char> is the pattern you're splitting on, not the piece you're getting back from split.

user_20690640
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