CODEWITHSUNDEEP
c++iostream
Nick
Nick

Reputation: 10539

How to output non null terminated string to iostream, but keep formatting

I am trying to output non null terminating string, but keep iomanip formatting, e.g. std::left, std::setw etc.

My current code looks like this:

inline std::ostream& operator << (std::ostream& os, const StringRef &sr){
    //return os.write(sr.data(), sr.size() );
    // almost the same, but std::setw() works
    return __ostream_insert(sr.data(), sr.size() );
}

This work OK on Linux with gcc, but fail on MacOS with clang.

Upvotes: 0

Views: 464

Answers (1)

Nick
Nick

Reputation: 10539

The suggestion about os.rdbuf()->sputn(seq, n) was certainly interesting, but it did not made the expected result.

I did open GCC C++ library code and "stole" from there. After the cleanup, code is something like this:

inline std::ostream& operator << (std::ostream& os, const StringRef &sr){
    // following is based on gcc __ostream_insert() code:
    // https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.2/ostream__insert_8h-source.html

    std::streamsize const width = os.width();
    std::streamsize const size  = static_cast<std::streamsize>( sr.size() );
    std::streamsize const fill_size = width - size;

    bool const left = (os.flags() & std::ios::adjustfield) == std::ios::left;

    auto osfill = [](std::ostream& os, auto const count, char const c){
        for(std::streamsize i = 0; i < count; ++i)
            os.put(c);
    };

    if (fill_size > 0 && left == false)
        osfill(os, fill_size, os.fill());

    os.write(sr.data(), size);

    if (fill_size > 0 && left == true)
        osfill(os, fill_size, os.fill());

    return os;
}

Upvotes: 2

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