Passing 2d C Array to LabVIEW

2d-c-array.dll

2d-c-array.png

2d-c-array.vi

c-2d-array.c

#include <stdlib.h>

#define DLL_EXPORT __declspec(dllexport)

int width = 20;
int height = 15;

unsigned char *data = NULL;

void DLL_EXPORT init()
{
    if (data == NULL)
    {
        data = (char *)malloc(width * height * 3);
        // write some dummy values into data
        for(int p =0; p< (height*width*3); ++p){
            *(data+p) = (unsigned char)(p%256); 
        }
    }
}

void DLL_EXPORT get_RGB_Array(const char *url, unsigned char **RGBarray, int *height_ptr, int *width_ptr)
{
    *height_ptr = height;
    *width_ptr = width;
    *RGBarray = data; 
}

void DLL_EXPORT deinit()
{
    if(data != NULL){
        free(data);
        data = NULL;
    }
}

This is in reference to this stackoverflow question

The labVIEW runtime exports a function called MoveBlock which works like memcpy and allows you to copy data from a pointer to another pointer.

This means we can copy the data from the pointer provided by get_RGB_Array() into a pre-sized labVIEW array.

There are other options and you can follow the later sections of these notes to learn about being able to manipulate LabVIEW allocated memory from you C-code in this how-to guide