Trouble casting 1D array to 2D array

Question

EDIT: C++ bits removed to avoid confusion

I have an array of data like so

int numSamples = 16;
float *lData  = (float*)calloc(numSamples, sizeof(float));

...and I would like to pass this data into a function with a definition like this . . .

void processSampleBlock (const float ** inputChannelData,
                         int    numInputChannels,
                         ...)

As you can see, this function accepts a 2D array, that can have multiple channels. My data is only a single channel (1D), but I can get the code to compile fine by doing a cast like this . .

processSampleBlock ((const float**)(lData),
                            1,
                            ...)

However, I get a bad access error at runtime then code within the function block attempts to dereference the data within the function . .

for (int nn=0; nn< numSamples; ++nn)
{
    float x = inputChannelData[0][nn]; //--> Computer says no
}

I am useless with C style multi-dimensional arrays and am probably making a fundamental error here. Any help would be great! Thanks

Why can't the array of pointers to the rows just contain a single pointer to a single row? — learnvst
– learnvst, Commented May 25, 2012 at 11:09
@learnvst - if you compile C-style code with a C++ compiler, it's not C code. These are two languages with subtle differences. If you intend to get a C++ answer, tag it as C++. — moooeeeep
– moooeeeep, Commented May 25, 2012 at 11:16

Daniel · Accepted Answer · 2012-05-25 11:26:29Z

5

You need to give it a pointer to an array of rows, so of you have one row give it a pointer to that row:

float *data = ...;
processSampleBlock(&data, 1);

edited May 25, 2012 at 11:26

answered May 25, 2012 at 10:58

Daniel

31.8k19 gold badges87 silver badges145 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Daniel Over a year ago

@Bo, he said he has only 1 channel

learnvst Over a year ago

lData.get() returns a pointer. The syntax you posted gives a compiler error

learnvst Over a year ago

I have edited the question to remove all of the potentially confusing boosty stuff.

Collectives™ on Stack Overflow

Trouble casting 1D array to 2D array

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related