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I'm working with a structure IMAGE_T (shown below, excuse the French) with its own alloc function. 

typedef struct {
    int nbl;        /* nombre de ligne de l'image */
    int nbc;        /* nombre de colonnes de l’image */
    unsigned char **data;   /* tableau bidim des pixels de l’image */
} IMAGE_T;



IMAGE_T *alloc_image(int nbl, int nbc){
    int taille = nbl*nbc+100;
    IMAGE_T * image;
    image = (IMAGE_T *) calloc(taille, sizeof(unsigned char)); 
    return image;
}

When going through the debugger, it bugs out stating: "unhandled exception at: 0xc0000005: access violation reading location 0x00000000." ..which I'm pretty sure relates to alloc_image not functioning properly. Any suggestions?

(And for further info, after declaring an IMAGE_T I'm then use another function that returns IMAGE_T *, which itself contains the function alloc_image within it, in order to allocate the memory. Is there anything wrong with this?)

Thanks

freewilly
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1 Answers1

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I suspect the reason you're getting an access violation is because you're trying to work with the "data" member which calloc() would have made null when allocating the memory.

That said, I'd like to understand why the "data" member in IMAGE_T is a unsigned char **? Why not simply a unsigned char *? (And then, alloc_image must allocate memory to IMAGE_T and then, within that allocated structure, allocate space for the "data".)

ShaunB
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  • It's unsigned char** as data later has, err, data put into it as a 2D array (viz. data[i][j]). When I debug it, `IMAGE_T * imagein = NULL;` comes up with 'imagein = 0xcccccccc {nbl=??? nbc=??? data=??? }' – freewilly Jan 08 '13 at 23:36