Trio is a fully matured and stable set of printf and string functions
designed be used by applications with focus on portability or with
the need for additional features that are not supported by standard
stdio implementation.

There are several cases where you may want to consider using trio:

    1. Portability across heterogeneous platforms.
    2. Embedded systems without stdio support.
    3. Extendability of unsupported features.
    4. Your native version doesn't do everything you need.

When you write applications that must be portable to a wide range
of platforms you often have to deal with inadequate implementations
of the stdio library functions. Most notably is the lack of secure
formatting functions, such as snprintf, or the lack of parameter
reordering commonly used for the internationalization of applications,
such as the <num>$ modifier. Sometimes the feature you need is
simply not present in stdio. So you end up spending much effort on
determining which platforms supports what, and to write your own
versions of various features. This is where trio can help you. Trio
is a platform-independent implementation of the stdio printf and
scanf functions and the string library functions.

The functionality described in the stdio standards is a compromise, and
does unfortunately not include a mechanism to extend the functionality
for an individual application. Oftentimes an application has the need
for an extra feature, and the application code can become much more
clear and readable by using an extension mechanism. Trio supports a
range of useful extensions such as user-defined specifiers, passing of
arguments in arrays, localized string scanning, thousand-separators,
and arbitrary integer bases.

Trio fully implements the C99 (ISO/IEC 9899:1999) and UNIX98 (the
Single Unix Specification, Version 2) standards, as well as many
features from other implemenations, e.g. the GNU libc and BSD4.

Examples

1. Output an integer as a binary number using a trio extension.

    trio_printf("%..2i\n", number);

2. Output a number with thousand-separator using a trio extension

    trio_printf("%'f\n", 12345.6);

The thousand-separator described by the locale is used.

3. Output an fixed length array of floating-point numbers.

    double array[] = {1.0, 2.0, 3.0}; printf("%.2f %.2f %.2f\n",
    array[0], array[1], array[2]);

The same with two trio extensions (arguments are passed in an array,
and the first formatting specifier sets the sticky option so we
do not have to type all the formatting modifiers for the remaining
formatting specifiers)

    trio_printfv("%!.2f %f %f\n", array);

Another, and more powerful, application of being able to pass arguments
in an array is the creation of the printf/scanf statement at run-time,
where the formatting string, and thus the argument list, is based on
an external configuration file.

4. Parse a string consisting of one or more upper-case alphabetic
   characters followed by one or more numeric characters.

    sscanf(buffer, "%[A-Z]%[0-9]", alphabetic, numeric);

The same but with locale using a trio extension.

    trio_sscanf(buffer, "%[:upper:]%[:digit:]", alphabetic, numeric);

Send feedback and patches to the git repo:

    https://github.com/orbea/trio

Trio web page:

    https://daniel.haxx.se/projects/trio/