How do I cast a void pointer to a int[3]? - c++

Question

I need to call a 3rd party library and pass in an int[3] as a void * like this [works]:
int pattern[3] = {2,4,10};
if ( OSTaskCreate( BlinkLED,
( void * ) pattern,
( void * ) &BlinkTaskStack[USER_TASK_STK_SIZE],
( void * ) BlinkTaskStack,
MAIN_PRIO - 1 ) != OS_NO_ERR )
{
iprintf( "*** Error creating blink task\r\n" );
}
But now I need to parse a string to get the pattern array and I can't seem to get it right.
First I pass the string into the parser and get back the array:
int (&ParseBlinkOnCommand(char rxbuffer[3]))[3]
{
// Code parses rxbuffer and creates the 3 ints needed
int pattern[3] = {repeats, onTicks, offTicks};
return pattern;
}
Then I try to pass it to the OSTaskCreate just like I did before:
int pattern2[3] = ParseBlinkOnCommand(rxbuffer);
if ( OSTaskCreate( BlinkLED,
( void * ) pattern2,
( void * ) &BlinkTaskStack[USER_TASK_STK_SIZE],
( void * ) BlinkTaskStack,
MAIN_PRIO - 1 ) != OS_NO_ERR )
{
iprintf( "*** Error creating remote blink task\r\n" );
}
but I get the error 'array must be initialized with a brace-enclosed initializer'.
What is the right way to do this?

Answer 1

First, ParseBlinkOnCommand returns reference to local object and so return dangling reference.
Second C-array are not copyable, so int pattern2[3] = ParseBlinkOnCommand(rxbuffer); should be int (&pattern2)[3] = ParseBlinkOnCommand(rxbuffer);.
but why not using std::vector or std::array (or custom structure) ?
std::vector<int> ParseBlinkOnCommand(const char (&rxbuffer)[3])
{
// Code parses rxbuffer and creates the 3 ints needed
return {repeats, onTicks, offTicks};
}
And then
auto pattern2 = ParseBlinkOnCommand(rxbuffer);
if ( OSTaskCreate( BlinkLED,
pattern2.data(),
&BlinkTaskStack[USER_TASK_STK_SIZE],
BlinkTaskStack,
MAIN_PRIO - 1 ) != OS_NO_ERR )
{
iprintf( "*** Error creating remote blink task\r\n" );
}