/ 
C-Blocks-0.42
River stage one • 1 direct dependent • 2 total dependents
/ C::Blocks::StretchyBuffer

NAME

C::Blocks::StretchyBuffer - Enabling stretchy buffers in your context

SYNOPSIS

use C::Blocks;
use C::Blocks::StretchyBuffer;

# Create a function that uses stretchy buffers:
$context->code('Body') = C::TinyCompiler::line_number(__LINE__) . q{
    void test_func() {
        /* stretchy buffers always start and end as null pointers */
        double * list = 0;
        
        /* Push some values onto the list */
        sbpush(list, 3.2);
        sbpush(list, -2.9);
        sbpush(list, 5);
        
        /* Eh, let's change that last one */
        list[2] = 22;
        
        /* Allocate room for five more */
        sbadd(list, 5);
        
        /* Get the list length */
        printf("List has %d available elements\n", sbcount(list));
        
         /* Set the last element */
        sblast(list) = 100;
        
        /* Pop the last element */
        printf("Last element was %f\n", sbpop(list));
        
        /* How many elements do we have? */
        printf("After a pop, we have %d available elements\n", sbcount(list));
        
        /* Remove two elements */
        int remaining = sbremove(list, 2);
        printf("sbremove returned %d\n", remaining);
        
        printf("After remove, we have %d available elements\n", sbcount(list));
        
        int i;
        printf("List:\n");
        for (i = 0; i < sbcount(list); i++) {
            printf("%d: %f\n", i, list[i]);
        }
        
        /* When we're all done, free the memory, restoring the value to null */
        sbfree(list);
    }
};

# Compile and call:
$context->compile;
$context->call_void_function('test_func');

DESCRIPTION

This C::TinyCompiler package provides Sean Barrett's implementation of stretchy buffers, as well as a couple of extensions by David Mertens for popping and removing values off the end. For more of Sean Barrett's cool work, see his website at http://nothings.org/.

How do you begin? Always start by declaring a null pointer of whatever type you want, like so:

int * data = 0;
char * input = 0;
special_type * array_of_structs = 0;

You then allocate memory using sbpush and sbadd. Thanks to the magic of preprocessor macros, accessing data in stretchy buffers is completely identical to accessing data from a normal array. The difference between the two is the way that memory is managed for you (or not):

/* Memory allocation is less verbose and includes the assertion */
double * observations = 0;
sbadd(observations, 20);
/* Iterating over values is identical */
int i;
for (i = 0; i < 20; ++i) {
    observations[i] = get_observation(i);
}
/* Different function for cleanup */
sbfree(observations);

/* Memory allocation is more verbose */
double * observations = (double *) malloc (20 * sizeof(double));
assert(observations);
/* Iterating over values is identical */
for (i = 0; i < 20; ++i) {
    observations[i] = get_observation(i);
}
/* Different function for cleanup */
free(observations);

Again, the really cool part about stretchy buffers is that they automatically handle extending the memory block when you push values or request the addition of more space on the 'far' end. That is, pushing and popping data off the end is easy and relatively fast (though shifting and unshifting off the front is not provided).

C::TinyCompiler::StretchyBuffer provides the following interface:

sbpush (array, value)

Pushes the given value onto the array, extending it if neccesary. This returns the value that was just added to the list.

sbcount (array)

Returns the number of elements currently available for use.

sbadd (array, count)

Makes count more elements available, allocating more memory if necessary. This returns the address of the new section of memory.

sblast (array)

Returns the last available element in the array, an lvalue! Note that this assumes that the array is not null, so only call this when you know your array is allocated.

sbpop (array)

Returns (the value of) the last available element in the array (or zero if the array is empty), reducing the array length by 1 (unless the array is empty). This does not deallocate the memory, however; that sticks around in case you later perform a push or add.

sbremove (array, count)

Removes count elements from the array, or if count is greater than the number of elements, empties the array. As with pop, this does not deallocate any memory but rather holds onto it in case it can be used for a later push or add. As an unplanned but pleasant side-effect, it returns the number of elements that remain after the removal.

sbfree (array)

Frees the memory associated with the stretchy buffer, if any is allocated. It always returns 0.

AUTHORS

Sean Barrett, http://nothings.org/ David Mertens, <dcmertens.perl at gmail.com>

BUGS

Please report any bugs or feature requests at the project's main github page: http://github.com/run4flat/perl-TCC/issues.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc C::TinyCompiler::StretchyBuffer

You can also look for information at:

ACKNOWLEDGEMENTS

Sean Barett, of course, for creating such a simple but useful chunk of code, and for putting that code in the public domain!

LICENSE AND COPYRIGHT

Sean Barett's original code is in the public domain. All modifications made by David Mertens are Copyright 2012 Northwestern University and 2015 Dickinson College.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.