px4_autopilot/apps/systemlib/uthash/doc/utstring.txt

utstring: dynamic string macros for C 
=====================================
Troy D. Hanson <thanson@users.sourceforge.net>
v1.9.5, November 2011

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Introduction
------------
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A set of very basic dynamic string macros for C programs are included with
uthash in `utstring.h`.  To use these macros in your own C program, just
copy `utstring.h` into your source directory and use it in your programs.

  #include "utstring.h"

The dynamic string supports basic operations such as inserting data (including
binary data-- despite its name, utstring is not limited to string content),
concatenation, getting the length and content, and clearing it.  The string
<<operations,operations>> are listed below.

Download
~~~~~~~~
To download the `utstring.h` header file, follow the link on the
http://uthash.sourceforge.net[uthash home page]. 

BSD licensed
~~~~~~~~~~~~
This software is made available under the 
link:license.html[revised BSD license]. 
It is free and open source. 

Platforms
~~~~~~~~~
The 'utstring' macros have been tested on:

 * Linux, 
 * Windows, using Visual Studio 2008 and Visual Studio 2010

Usage 
-----

Declaration
~~~~~~~~~~~

The dynamic string itself has the data type `UT_string`.  It is declared like,

  UT_string *str;

New and free
~~~~~~~~~~~~
The next step is to create the string using `utstring_new`. Later when you're
done with it, `utstring_free` will free it and all its content. 

Manipulation
~~~~~~~~~~~~
The `utstring_printf` or `utstring_bincpy` operations insert (copy) data into
the string. To concatenate one utstring to another, use `utstring_concat`.  To
clear the content of the string, use `utstring_clear`. The length of the string
is available from `utstring_len`, and its content from `utstring_body`. This 
evaluates to a `char*`.  The buffer it points to is always null-terminated.
So, it can be used directly with external functions that expect a string.
This automatic null terminator is not counted in the length of the string.

Samples
~~~~~~~

These examples show how to use utstring.

.Sample 1
-------------------------------------------------------------------------------
#include <stdio.h>
#include "utstring.h"

int main() {
    UT_string *s;

    utstring_new(s);
    utstring_printf(s, "hello world!" );
    printf("%s\n", utstring_body(s));

    utstring_free(s);
    return 0;
}
-------------------------------------------------------------------------------

The next example is meant to demonstrate that printf 'appends' to the string.
It also shows concatenation.

.Sample 2
-------------------------------------------------------------------------------
#include <stdio.h>
#include "utstring.h"

int main() {
    UT_string *s, *t;

    utstring_new(s);
    utstring_new(t);

    utstring_printf(s, "hello " );
    utstring_printf(s, "world " );

    utstring_printf(t, "hi " );
    utstring_printf(t, "there " );

    utstring_concat(s, t);
    printf("length: %u\n", utstring_len(s));
    printf("%s\n", utstring_body(s));

    utstring_free(s);
    utstring_free(t);
    return 0;
}
-------------------------------------------------------------------------------

The last example shows how binary data can be inserted into the string. It also
clears the string and prints new data into it.

.Sample 3
-------------------------------------------------------------------------------
#include <stdio.h>
#include "utstring.h"

int main() {
    UT_string *s;
    char binary[] = "\xff\xff";

    utstring_new(s);
    utstring_bincpy(s, binary, sizeof(binary));
    printf("length is %u\n", utstring_len(s));

    utstring_clear(s);
    utstring_printf(s,"number %d", 10);
    printf("%s\n", utstring_body(s));

    utstring_free(s);
    return 0;
}
-------------------------------------------------------------------------------

[[operations]]
Reference
---------
These are the utstring operations. 

Operations
~~~~~~~~~~

[width="100%",cols="50<m,40<",grid="none",options="none"]
|===============================================================================
| utstring_new(s) | allocate a new utstring
| utstring_renew(s) | allocate a new utstring (if s is `NULL`) otherwise clears it
| utstring_free(s) | free an allocated utstring
| utstring_init(s)  |  init a utstring (non-alloc)
| utstring_done(s) |  dispose of a utstring (non-allocd)
| utstring_printf(s,fmt,...) | printf into a utstring (appends)
| utstring_bincpy(s,bin,len) | insert binary data of length len (appends)
| utstring_concat(dst,src) | concatenate src utstring to end of dst utstring
| utstring_clear(s) | clear the content of s (setting its length to 0)
| utstring_len(s) | obtain the length of s as an unsigned integer
| utstring_body(s) | get `char*` to body of s (buffer is always null-terminated)
|===============================================================================

Notes
~~~~~

1. `utstring_new` and `utstring_free` are used to allocate a new string and free it,
   while `utstring_init` and `utstring_done` can be used if the UT_string is already
   allocated and just needs to be initialized or have its internal resources
   freed.
2. `utstring_printf` is actually a function defined statically in `utstring.h`
   rather than a macro.

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