Flipping Vertices with C - c

Question

I am trying to flip an image in C vertically so if the image is < it will end up > and my function includes
//Setting the struct up for the pixel's
struct pixel
{
unsigned char red;
unsigned char green;
unsigned char blue;
};
//Setting the struct up for the Image Type and scanning in the pxiels into an array
struct ImageType
{
char ppImage[3];
char comment[256];
char newlinechar;
int width, height;
int maxColor = 255;
struct pixel image[100][100];
};
//Function in order to flip the image, going from the left most pixel flipping with the right most
void MirrorVertical(struct ImageType imgur)
{
int x,y;
const int middle = imgur.width / 2;
struct pixel tmp;
struct *pixel p;
for(y=0; y < imgur.height; ++y)
{
p = tmp + y * imgur.width;
for(x=0; x < middle; ++x)
{
tmp = p[x];
p[x] = p[imgur.width - 1 - x];
p[imgur.width - 1 - x] = tmp;
}
}
}
I got my structs to work but for some reason my function will not output it, I am scanning in the image into from a struct so....
//Scanning in the pixels for the first image
for(i=imageA.height-1; i <= 0; i--)
{
for(j=0; j < imageA.width; j++)
{
scanf("%hhu", &imageA.image[i][j].red);
scanf("%hhu", &imageA.image[i][j].green);
scanf("%hhu", &imageA.image[i][j].blue);
}
}
What am I doing wrong in my function?
It should be
for(x=0; x < width; x++)
{
for(y = 0; y < height/2; y++)
{
temp = imgur.image[x][y];
imgur.image[x][y] = imgur.image[x][height-y-1]
imgur.image[x][height-y-1] = temp;
}
}
}

Answer 1

Shouldn't this: for(i=imageA.height-1; i <= 0; i--) be for(i=imageA.height-1; i >= 0; i--)? (in the "scanning in the pixels for the first image" code)

Answer 2

I imagine your compiler must be complaining about
struct pixel tmp;
struct *pixel p;
for(y=0; y < imgur.height; ++y)
{
p = tmp + y * imgur.width;
You are adding a struct to an int and allocating the result to a pointer. How is it supposed to work?
EDIT now that you have updated your question with "better" code and it's still not working, here are a few things you could / should change.
You declare a variable tmp then try to access temp. Recipe for failure
You pass the entire struct imgur to the function. That means "make a copy of everything". You should really pass a pointer to the object - change the prototype to reflect that, and access the elements as imgur->height etc
You never declare the variables height and width in your MirrorVertical function
(minor) you compute the value height - 1 - y twice per inner loop - 20000 times in total. If you swap the inner and outer loops and compute it just once (and assign to a new variable newY) you can save a little bit of time (not sure it it's really more efficient since you end up looping over X which might destroy cache coherence instead, especially with big images).
My compiler (and the C standard) complains about the statement int maxColor = 256; in the definition of the struct; you cannot initialize a value in the typedef.
Miscellaneous other errors thrown by the compiler.
I took the liberty of fixing many of them - that leads to the following code which appears to compile and run; now all you need is add your "input image" and "output image" functions (maybe).
#include <stdio.h>
//Setting the struct up for the pixels
struct pixel
{
unsigned char red;
unsigned char green;
unsigned char blue;
};
//Setting the struct up for the Image Type and scanning in the pixels into an array
struct ImageType
{
char ppImage[3];
char comment[256];
char newlinechar;
int width;
int height;
int maxColor; // cannot initialize this here; removed "=256"
struct pixel image[100][100];
};
//Function in order to flip the image, going from the left most pixel flipping with the right most
void MirrorVertical(struct ImageType *imgur) // using a pointer to the struct
{
int x,y, height, width; // added declaration of height, width
// const int middle = imgur->width / 2; // removed, not used
struct pixel tmp; // use same name here and in loop
height = imgur->height; // initialize once - save a redirect later
width = imgur->width; // ditto
for(y = 0; y < imgur->height/2; y++) // made this the outer loop
{
int newY = height - y - 1; // so we only compute it once
for(x=0; x < imgur->width; x++)
{
tmp = imgur->image[x][y]; // use "tmp" not "temp"
imgur->image[x][y] = imgur->image[x][newY];
imgur->image[x][newY] = tmp;
}
}
}
// a simple main program… this doesn't really do anything except call the function
int main(void) {
struct ImageType i1;
// … need to add code to import the image
MirrorVertical(&i1); // note - passing POINTER to i1, not the entire struct
// … need to add code to export the image
}
Let me know if that works.