using malloc to create array of pointers

[Maulkin]

Is theis the correct code to create an array of pointers using malloc

b = malloc(256 * sizeof(char*));

if so how do I set the memory address pointed to by each pointer.
e.g

b[i] = &extract[i];

 

[smaniraja]

Ok, but few changes.

char **b;
b = (char **) malloc(256 * sizeof(char *));
put b[0] = (char *) malloc(noOfCharacters * sizeof(char));
or as u said
b = &extract;

If you want to allocate two dimensional arrays then do like the following.

int main()
{
int (*p)[3];
int i, j;
p = (int (*)[3]) malloc(sizeof(int) * 3 * 2);
for(i = 0; i < 2; i++)
{
for(j = 0; j < 3; j++)
{
p[j] = i * 3 + j;
}
}
return 0;
}

 

[RbgoWeb]

Here's a trick where you have a single dim array (e.g. bitmap bits); you like to keep it stored this way for easy writing back to disk.

//Before you can write bmp bits to it...
BYTE* lpBits;
lpBits = (BYTE *)calloc(biWidth * biHeight, sizeof(BYTE));

//Writing data from bmp file to lpBits
...here...

//It would be easy though to index the bmp in 2D, no?
//We create an array of byte pointers for each line...
BYTE** lppBits;
lppBits = (BYTE**)calloc(biHeight, sizeof(BYTE*));

//Now we set the pointers to the beginning of each row...
int R=0, iOffset=0;
while(R < biHeight){
lppBits[R] = &lpBits[iOffset];
iOffset += biWidth;
R++;
}

//Now you're able get each bmp color index like this...
BYTE tiColor;
int R, C;

R=0;
while(R < biHeight){
C=0;
while(C < biWidth){
tiColor= lppBits[R][C];
C++;
}
R++;
}