malloc doesn't allocate 3d array properly

Question

I am writing a program in c that would read the ppm input file and convert it to ASCII art. In the program, I alllocated a 3d array that would store the height and width of the input file and the RGB components. The array elements (pixels) would then be converted to grayscale and written into the output file as ASCII art. But when I tried to compile the following code the compiler warned me about that:

asciiArt.c: In function 'main':

asciiArt.c:48:32 error: expected expression before 'int':
   array = malloc(width*sizeof(**int));
                                 ^           
asciiArt.c:50:35: error: expected expression before 'int':
  array[0] = malloc(height*sizeof(*int)); 
                                   ^  

but the third malloc() seems to be right. Why? Can anyone tell me what am I doing wrong?

Here is my code:

#include <stdio.h>
#include <stdlib.h>

char method_of_conversion(int greyscale){
    if(greyscale >= 230){
        return ' ';
    }else if(greyscale >= 200 && greyscale < 230){
        return '.';
    }else if(greyscale >= 180 && greyscale < 200){
        return '\'';
    }else if(greyscale >= 160 && greyscale < 180){
        return ':';
    }else if(greyscale >= 130 && greyscale < 160){
        return 'o';
    }else if(greyscale >= 100 && greyscale < 130){
        return '&';
    }else if(greyscale >= 70 && greyscale < 100){
        return '8';
    }else if(greyscale >= 50 && greyscale < 70){
        return '#';
    }else if(greyscale < 50){
        return '@';
    }
}

int main(){
    char ppmFile[100];
    char outputFile[100];

    int window_size;

    scanf("%s", &ppmFile); 
    scanf("%s", &outputFile); 
    // the size of a window of pixels to convert to ascii art character
    scanf("%d", &window_size); 

    FILE *input = fopen(ppmFile, "rb");
    FILE *output = fopen(outputFile, "w"); 


    char header[5]; //header = P6
    fscanf(input, "%s\n", header);
    int width, height, maxPixel; // max pixel is always 255
    // read the header from the ppm file
    fscanf(input, "%d %d %d\n", &width, &height, &maxPixel);

    int ***array;
    array = malloc(width*sizeof(**int));

    array[0] = malloc(height*sizeof(*int));

    array[0][0] = malloc(3*sizeof(int));


    int x, y;
    for (x = 0; x < width; x++){ 
        for(y=0; y < height; y++){
            array[x][y][0] = fgetc(input); //red
            array[x][y][1] = fgetc(input); //green
            array[x][y][2] = fgetc(input); //blue

            int greyscale;
            int i, j;
            for(i = 0; i < width; i+=window_size){
                for(j=0; j < height; j+=window_size){
                    // greyscale = (red + green +blue)/3;
                    greyscale = (array[x][y][0] + array[x][y][1] +array[x][y][2])/(3*window_size*window_size);
                    char c = method_of_conversion(greyscale);
                    fprintf(output,"%c",c); // write the ASCII art directly in the output file
                }
            }   
        }fprintf(output,"\n");
    }

    free(array);
    fclose(input);
    fclose(output);

    return 0;
}

3d array is already a problem, also there is no such `sizeof(*int)`, it's `sizeof(int *)`, and to prevent the problem completely just do `int *x = malloc(count * sizeof(*x));`, which is ok because `x` is not a type name. — Iharob Al Asimi, May 22 '15 at 15:32
@iharob same opinion here. (Just see the last line of my answer.) :-D — Sourav Ghosh, May 22 '15 at 15:36

score 3 · Accepted Answer · edited May 23 '17 at 10:26

3

You can't write sizeof(*int) you have to write sizeof(int*).

Also, see this answer to see how to better create your array

edited May 23 '17 at 10:26

Community

1
1

answered May 22 '15 at 15:32

Eregrith

4,263
18
39

score 2 · Answer 2 · answered May 22 '15 at 15:32

In your code, you need to change

array = malloc(width*sizeof(**int));

to

array = malloc(width*sizeof(int**));

Similar for other case also, change sizeof(*int) to sizeof(int*).

That said, just a word of advice, PLease don't try to become a three-star programmer. Usually it's discouraged.

score 1 · Answer 3 · answered May 22 '15 at 15:42

1

To avoid errors like these, you can use the following pattern.

array = malloc(width*sizeof(*array));
array[0] = malloc(height*sizeof(*array[0]));

answered May 22 '15 at 15:42

R Sahu

204,454
14
159
270

malloc doesn't allocate 3d array properly

3 Answers3