How to get displayed width of a string?

When y开发者_运维知识库ou have non-fixed width characters (such as \t) in a string , or escape codes, such as those for ANSI color (such as \1xb[31m), these characters add to the .length() of an std::string, but do not add to the displayed length when printed.

Is there any way in C++ to get the displayed width of a string in *nix?

For instance:

displayed_width("a\tb") would be 4 if the displayed tab width is 2
displayed_width("\1xb[33mGREEN") would be 5

Most commonly, a tab asks the terminal program to move the cursor to a column that's a multiple of 8, though many terminal programs let you configure that. With such behaviour, how much width a tab actually adds depends on where the cursor was beforehand relative to the tab stops. So, simply knowing the string content is not enough to calculate a printable width without some assumption or insight regarding prior cursor placement and tab stops.

Non-printable codes also vary per terminal type, though if you only need ANSI colour then that's pretty easy. You can move along the string counting characters; when you see an ESCAPE skip through to the terminating m. Something like (untested):

int displayed_width(const char* p)
{
    int result = 0;
    for ( ; *p; ++p)
    {
        if (p[0] == '\e' && p[1] == '[')
            while (*p != 'm')
                if (*p)
                    ++p;
                else
                    throw std::runtime_error("string terminates inside ANSI colour sequence");
        else
            ++result;
    }
    return result;
}

Nothing built in. The "displayed width" of the tab character is an implementation detail, as are console escape sequences. C++ doesn't care about platform-specific things like that.

Is there something in particular you're trying to do? We may be able to suggest alternatives if we know what particular task you're working on.

Not with standard methods to my knowledge. C++ does not know about terminals. My guess would be to use NCURSES for that. Dunno if boost has something up the sleeve for that though.

Display length on what device? A console that uses a fixed-width font? A window that uses a proportional font? This is highly device-dependent question. There is no fixed answer. You will have to use the tools associated with the target output device.