xo_emit - Man Page

emit formatted output based on format string and arguments


Text, XML, JSON, and HTML Output Emission Library (libxo, -lxo)


#include <libxo/xo.h>

xo_emit(const char *fmt, ...);

xo_emit_h(xo_handle_t *xop, const char *fmt, ...);

xo_emit_hv(xo_handle_t *xop, const char *fmt, va_list vap);


The xo_emit() function emits formatted output using the description in a format string along with a set of zero or more arguments, in a style similar to printf(3) but using a more complex format description string, as described in xo_format(5).

xo_emit() uses the default output handle, as described in libxo(3), where xo_emit_h() uses an explicit handle. xo_emit_hv() accepts a va_list for additional flexibility.


In this example, a set of four values is emitted using the following source code:

    xo_emit(" {:lines/%7ju} {:words/%7ju} "
            "{:characters/%7ju} {d:filename/%s}\n",
            linect, wordct, charct, file);

Output can then be generated in various style, using the "--libxo" option:

    % wc /etc/motd
          25     165    1140 /etc/motd
    % wc --libxo xml,pretty,warn /etc/motd
    % wc --libxo json,pretty,warn /etc/motd
      "wc": {
        "file": [
            "lines": 25,
            "words": 165,
            "characters": 1140,
            "filename": "/etc/motd"
    % wc --libxo html,pretty,warn /etc/motd
    <div class="line">
      <div class="text"> </div>
      <div class="data" data-tag="lines">     25</div>
      <div class="text"> </div>
      <div class="data" data-tag="words">    165</div>
      <div class="text"> </div>
      <div class="data" data-tag="characters">   1140</div>
      <div class="text"> </div>
      <div class="data" data-tag="filename">/etc/motd</div>

Return Code

xo_emit returns a negative value on error. If the XOF_COLUMNS flag has been turned on for the specific handle using xo_set_flags(3), then the number of display columns consumed by the output will be returned.

See Also

xo_open_container(3), xo_open_list(3), xo_emit_f(3), xo_emit_field 3, xo_format(5), libxo(3)


The libxo library first appeared in FreeBSD 11.0.


libxo was written by Phil Shafer <phil@freebsd.org>.

Additional Documentation

FreeBSD uses libxo version 1.6.0. Complete documentation can be found on github:


libxo lives on github as:


The latest release of libxo is available at:



The libxo library was added in FreeBSD 11.0.


Phil Shafer

Referenced By

libxo(3), xo(1), xo_attr(3), xo_create(3), xo_emit_err(3), xo_err(3), xo_error(3), xo_finish(3), xo_flush(3), xo_format(5), xohtml(1), xolint(1), xo_message(3), xo_no_setlocale(3), xo_open_container(3), xo_open_list(3), xo_open_marker(3), xo_parse_args(3), xo_set_allocator(3), xo_set_flags(3), xo_set_info(3), xo_set_options(3), xo_set_style(3), xo_set_version(3), xo_set_writer(3).

December 4, 2014