Thread: resize image

You don't have to use an array of ints. You can create an array of your RGBTRIPLE structs:

Code:

RGBTRIPLE **image = malloc(rows * sizeof(*image));
for (i = 0; i < rows; i++) {
    image[0] = malloc(cols * sizeof(*image[0]));
}

for (i = 0; i < rows; i++) {
    if (fread(image[i], sizeof(image[i][j]), cols, inptr) != cols * sizeof(image[i][j])) {
        perror("fread failed on original image");
        return -1;  // or whatever error code you want
    }
}

I've changed your code a bit to my vars

Code:

    RGBTRIPLE **image = malloc(biHeight * sizeof(*image));
    for (i = 0; i < biHeight; i++)
        image[0] = malloc(bi.biWidth * sizeof(*image[0]));

    for (i = 0; i < biHeight; i++)
        for (j = 0; j < bi.biWidth; j++)
            if (fread(image[i], sizeof(image[i][j]), bi.biWidth, inptr) != bi.biWidth * sizeof(image[i][j]))
            {
                perror("fread failed on original image");
                return -1;  // or whatever error code you want
            }

But the line perror gets excuted all the time. I've seen your fread statement and everything seem right.
Both the height and the width get a value of 3. because my input bmp is 3 by 3.
What you cause it?

Did you look at the documentation to see what fread actually returns?

Originally Posted by lamko

I've changed your code a bit to my vars

Code:

    RGBTRIPLE **image = malloc(biHeight * sizeof(*image));
    for (i = 0; i < biHeight; i++)
        image[0] = malloc(bi.biWidth * sizeof(*image[0]));

    for (i = 0; i < biHeight; i++)
        for (j = 0; j < bi.biWidth; j++)
            if (fread(image[i], sizeof(image[i][j]), bi.biWidth, inptr) != bi.biWidth * sizeof(image[i][j]))
            {
                perror("fread failed on original image");
                return -1;  // or whatever error code you want
            }

But the line perror gets excuted all the time. I've seen your fread statement and everything seem right.
Both the height and the width get a value of 3. because my input bmp is 3 by 3.
What you cause it?

sizeof(image[i][j]) is going to return the size of the pointer to the array... not the size of the image in memory. You need to track that separately.

There are bugs in my code. Read it over carefully, and look at the documentation for malloc and fread. Pay attention to loop indices, and think about what makes sense and what doesn't. In particular:
1. I have a loop that malloc's each time. Where do I store each result? Where should it be stored?
2. When I read, I only have a single loop, but two indexes. Where did j come from and what's it's value?
3. How much are you reading (how many RGBTRIPLE's), and how many times are you doing that?

I've thought I was stuck but i've found this website : A Tutorial on Pointers and Arrays in C and it is explaining just the things I need to grasp all this stuff. Now of to master it

Just one small point here... It's not really necessary to cast the return value of malloc() in a C program, that's a C++ thing...
Malloc returns a void* that can be assigned to almost any pointer.