Thread: Writing an array to file

I've been trying for ages to get this code to work but it just presents me with a blank file every time. Any help is very much appreciated.

Code:

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


typedef struct
{
    int x, y;
} PPMImage;


typedef struct 
{
    int rgb_comp_colour;
    char buff[16];
    char filetype[2];
    int height;
    int width;
} PPMHead;


PPMHead head[3];
int **Array; //Double pointer defines as a pointer pointing to a pointer that is pointing to an integer


int main(void)
{
    FILE *fp;
    char fname[100];
    printf("Enter file name: ");
    scanf("%s", fname);
    fseek(stdin,0,SEEK_END);
    fp = fopen(fname, "r");
    if (fp == NULL)
    {   
        printf("\tError while opening the file\n");
    }                        
    else    
    {
        printf("\tReading in %s\n", fname);
    }


    Array = malloc(head[0].width*sizeof(int*)); //Points to malloc
    for (int i=0;i<head[0].width;i++)
    {
        Array[i] = (int*)malloc(head[0].height*sizeof(int));
    }
    for(int j=0;j<head[0].height;j++)
    {
        for(int i=0;i<head[0].width;i++)
        {
            fscanf(fp, "%3d ", &Array[i][j]); //Scans the address of Array[i][j]
        }
    }    
    fclose(fp);


    //Save PPM Array Into New PPM File
    FILE *pf;
    int i, j;
    char fname2[100];
    printf("Enter file name: ");
    scanf("%s", fname2);
    fseek(stdin,0,SEEK_END);
    pf = fopen(fname2, "w");
    if (pf == NULL)
    {   
        printf("\tError while opening the file\n");
    }
    else    
    {
        printf("\tWriting in %s\n", fname2);
    }


       for(j=0;j<head[0].height;j++)
        {
            fprintf(pf, "\n");
            for(i=0;i<head[0].width;i++)
            {
                fprintf(pf, "%3d ", Array[i][j]);
                //fprintf(pf, "%3d ", (Array+j*head[0].width + i));
            }
        } 


    fclose(pf);
    free(Array);
    return 0;
}

I can see that you're using head[0].width and head[0].height without initializing head, which means they're always zero, as head is global. This means that your loops do not execute even a single time.

Can you please post the code where you initialize it if you do? Also, you need to use the extern storage class if you do so, or otherwise initialize head before reading from it.

Ohhhh. I see. How would I initialise it? Is it similar to initialising a pointer?

Originally Posted by erikkonstas

Initializing a struct means initializing each of its members, for example:

Code:

#include <stdio.h>

typedef struct
{
    int x;
    int y;
    int z;
} point3d;


int main(void)
{
    // Declaration
    point3d p;

    // Initialization
    p.x = 1;
    p.y = 2;
    p.z = 3;

    // Reading of members
    printf("The point is (x = %d, y = %d, z = %d).\n", p.x, p.y, p.z);

    return 0;
}

As for your case, you would want to use appropriate data to initialize head[0], head[1], etc. By the way, you may want to consider not declaring it globally, but inside main.

P.S.: There are more ways to initialize a struct variable, but initializing each member on its own is the clearest.

Code:

typedef struct 
{
    int rgb_comp_colour;
    char buff[16];
    char filetype[2];
    int height;
    int width;
} PPMHead;


PPMHead head[3];
head.height = 1;
head.width = 2;
head.filetype = 3;

Thanks. I have done it like this but it tells me that . should be a ;

Is it me doing it wrong or my program? I would assume its me.

Originally Posted by DGB_684

Thanks. I have done it like this but it tells me that . should be a ;

head isn't a PPMHead, but an array of PPMHead. You have to initialize each element of head separately (that is, the members of head[0], the members of head[1], etc.), and in a function (not outside like you have it right now). Also, you need to put the correct data in the members, e.g. head[0].filetype is a char[2], so you can't assign 3 to it. Unfortunately, I can't know what said correct data would be in your case.

I changed it to this but I still don't think its right. The point of this program is to read in (pixel) values from a ppm file, store them in an array and then write them into a file. So I want the 2d array I've malloced to point to the image structure I guess...? It doesn't really work as a function for me but I can't have it in my main function because this is a small part of a bigger project.

Code:

void head()
{
    PPMHead head[0];
    head[0].height;
    head[0].width;
    head[0].filetype;
}