Thread: Need some help initializing an array

Hi, Im trying to initialize the counter array to all zeros, but I keep getting this error when trying to compile:

xray.cpp:30: error: variable-sized object ‘counter’ may not be initialized

Code:

#include <iostream>
#include <stdio.h>
#include "CImg.h"


using namespace cimg_library;

//main program
int main()
{
CImg<double> img("xray.jpg");

//retrieve image dimensions
const unsigned int width = img.dimx();
const unsigned int height = img.dimy();

//converts the image to black and white
img.RGBtoYCbCr().channel(0).resize(-100,-100,1,3).RGBtoLUT(CImg<>(2,1,1,3).fill(0.0f,255.0f),false); 

//displays image
CImgDisplay display(img,"Black and White");
while (!display.is_closed)
display.wait();

//display dimensions
printf("The height of the image is %d\n",height);
printf("The width of the image is %d\n",width);

//initialize counter array of size height
int counter[height]={0};

//go through image one row at a time from left to right
for (int i=0;i<width;i++)
{
    for (int j=0;j<height;j++)
    {
	 //if pixel equals white
	 //add total number of white pixels to counter  
            
    }
}

return 0;
}

The error message seems pretty clear: you cannot initialize a variable-length object. (I.e., initialization is a compile-time activity, and the compiler has no idea what length is going to be in the future.) You'll have to use a loop.

Originally Posted by tabstop

The error message seems pretty clear: you cannot initialize a variable-length object. (I.e., initialization is a compile-time activity, and the compiler has no idea what length is going to be in the future.) You'll have to use a loop.

thats tabstop, that makes sense. I have one last question Im stumped on. Im trying to calculate the number of white pixels per row, but so far I can only get it calculate the total number of white pixels in the image. How do I make it calculate the total number of white pixels per row? Here is the code I have so far:

Code:

#include <iostream>
#include <stdio.h>
#include "CImg.h"
#include <vector>

using namespace cimg_library;


//main program
int main()
{
CImg<float> img("xray.jpg");

const unsigned int width = img.dimx();
const unsigned int height = img.dimy();

//converts the image to black and white
img.RGBtoYCbCr().channel(0).resize(-100,-100,1,3).RGBtoLUT(CImg<>(2,1,1,3).fill(0.0f,255.0f),false); 

//displays image
CImgDisplay display(img,"Black and White");
while (!display.is_closed)
display.wait();


printf("The height of the image is %d\n",height);
printf("The width of the image is %d\n",width);

//counter array
int counter[height];
int number = 0;

//go through image left to right, top to bottom
for (int i=0;i<width;i++)
{
    for (int j=0;j<height;j++)
    {
	 //if pixel equals white, add to number
	 if (img(i,j,0,0) == 255 && img(i,j,0,1) == 255 && img(i,j,0,2) == 255)
	 {
		 number=number + 1;
	 }

    }
}
printf("The number of white pixels is %d\n", number);

int x;

//for each row, print the total number of white pixels for that row
for (x =0; x < height; x++)
{
	printf("%d %d\n", x, number);
}

return 0;
}

So, you're looping over the entire image. Don't do that, if you only want to look at a single row.

BTW, variable length arrays like the one you're using aren't legal in standard C++, they are just provided as an extension on some the gcc compiler (because they are in the latest C standard).

Normally, in standard C++ you'd use a vector for a dynamically sized array. The vector is automatically initialized with the loop.