Segmentation Fault?

[ostangel]

I have been learning C for about a month or so and right now:

I am trying to write a C program that will read a pixmap image in PGM file format and then rotate the image 180 degrees. I have the code written out, but when I try to run it, it tells me I have segmentation fault. I have been trying to figure it out for hours and even debug it. When debugging, it points me to the line: pointer[i] = (int) calloc(N, sizeof(int));

But I can't figure out how to fix it. Any help much appreciated! Code below..

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

/* M is the height of the image and N the width */
int ** memAlloc(int M, int N)
{
    int i;
    int ** pointer;

    pointer = NULL;
    pointer = (int **) calloc(M, sizeof(int));

    if(pointer = NULL)
    {
        printf("Memory Allocation unsuccessful");
    }

    for(i = 0; i < M; i++)
    {
        pointer[i] = (int *) calloc(N, sizeof(int));
        
        if(pointer[i] == NULL)
        {
            printf("Memory Allocation Unsuccessful");
        }
    }

    return pointer;
}

void inFile(char fn[], int **temp, int M, int N)
{
    int i, j, k;
    char ch[4]; /* header information */

    unsigned int value;
    FILE * fp;
    fp = NULL; /* initialization of pointer */

    fp = fopen(fn, "r");

    if(fp == NULL)
    {
        printf("File not opened");
        exit(1);
    }

    /* ch[0] and ch[1] holds the version. i holds the width, j holds the height and k holds the max gray value */
    fscanf(fp, "%c%c\n%d %d\n%d", &ch[0], &ch[1], &i, &j, &k);

    for (i = 0; i < M; i++)
    {
        for(j = 0; j < N; j++)
        {
            fscanf(fp, "%d", &value);
            temp[i][j] = value;
        }
    }

    fclose(fp);
}

void outFile(char outfile[], char c, int v, int N, int M, int max, int ** img)
{
    int i, j;
    FILE * fout;
    fout = NULL; /* initialization of pointer */

    fout = fopen(outfile, "w");

    /* writes the header of the image */
    fprintf(fout, "%c%d\n", c, v);
    fprintf(fout, "%d %d\n", N, M);
    fprintf(fout, "%d\n", max);

    if(fout == NULL)
    {
        printf("\n Error Opening Output File");
        //getch();
        exit(1);
    }

    /* rotate image by 180 degrees */
    for(i = 23; ((i < M) && (i >= 0)); i--)
    {
        for(j = 6; ((j < N) && (j >= 0)); j--)
        {
            fprintf(fout, "%d ", img[i][j]);
        }
    }

    /* for(i = 0; i < M; i++)
    {
        for(j = 0; j < N; j++)
        {
            fprintf(fout, "%d ", img[i][j]);
        }
    } */

    close(fout);
}

int main(int argc, char* argv[])
{
    int i, j;
    int M, N; /* M is the height, N is the width */
    int ** img = 0;
    FILE *file;
    
    file = NULL; /* initialization of pointer */
    
    char c; /* first character of the header */
    int v, max; /* v holds the version */

    char infile[25];
    char outfile[25];

    printf("\nInput File Name(25 characters MAX with .pgm extension) :: ");
    gets(infile);

    printf("\nOutput File Name(25 characters MAX with .pgm extension) :: ");
    gets(outfile);

    file = fopen(infile, "r");

    if(file == NULL)
    {
        printf("File not opened");
        //getch();
        exit(1);
    }

    fscanf(file, "%c%d\n%d %d\n%d", &c, &v, &N, &M, &max);
    fclose(file);

    img = memAlloc(M, N);

    inFile(infile, img, M ,N);
    outFile(outfile, c, v, N, M, max, img);
    system("PAUSE");
    return 0;
}

[Rubberman]

The problem is here:

    pointer = (int **) calloc(M, sizeof(int));

It should be

    pointer = (int **) calloc(M, sizeof(int*));

Because an int may be smaller than an int*, you are probably walking on your heap in the loop where you allocate each row.

[ostangel]

The problem is here:

    pointer = (int **) calloc(M, sizeof(int));

It should be

    pointer = (int **) calloc(M, sizeof(int*));

Because an int may be smaller than an int*, you are probably walking on your heap in the loop where you allocate each row.

Thanks for the reply! unfortunately, I'm still getting a segmentation fault.

[Rubberman]

Thanks for the reply! unfortunately, I'm still getting a segmentation fault.

So, post your code changes.

[ostangel]

So, post your code changes.

I basically just implemented your previous suggestion I.e. Instead of int, I did int* but it is still somehow giving me a segmentation fault.

[Rubberman]

I basically just implemented your previous suggestion I.e. Instead of int, I did int* but it is still somehow giving me a segmentation fault.

I've heard that before, but as we say, the devil's in the details!

[ostangel]

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

/* M is the height of the image and N the width */
int ** memAlloc(int M, int N)
{
    int i;
    int ** pointer;

    pointer = NULL;
    pointer = (int **) calloc(M, sizeof(* int));

    if(pointer = NULL)
    {
        printf("Memory Allocation unsuccessful");
    }

    for(i = 0; i < M; i++)
    {
        pointer[i] = (int *) calloc(N, sizeof(int));
        
        if(pointer[i] == NULL)
        {
            printf("Memory Allocation Unsuccessful");
        }
    }

    return pointer;
}

void inFile(char fn[], int **temp, int M, int N)
{
    int i, j, k;
    char ch[4]; /* header information */

    unsigned int value;
    FILE * fp;
    fp = NULL; /* initialization of pointer */

    fp = fopen(fn, "r");

    if(fp == NULL)
    {
        printf("File not opened");
        exit(1);
    }

    /* ch[0] and ch[1] holds the version. i holds the width, j holds the height and k holds the max gray value */
    fscanf(fp, "%c%c\n%d %d\n%d", &ch[0], &ch[1], &i, &j, &k);

    for (i = 0; i < M; i++)
    {
        for(j = 0; j < N; j++)
        {
            fscanf(fp, "%d", &value);
            temp[i][j] = value;
        }
    }

    fclose(fp);
}

void outFile(char outfile[], char c, int v, int N, int M, int max, int ** img)
{
    int i, j;
    FILE * fout;
    fout = NULL; /* initialization of pointer */

    fout = fopen(outfile, "w");

    /* writes the header of the image */
    fprintf(fout, "%c%d\n", c, v);
    fprintf(fout, "%d %d\n", N, M);
    fprintf(fout, "%d\n", max);

    if(fout == NULL)
    {
        printf("\n Error Opening Output File");
        //getch();
        exit(1);
    }

    /* rotate image by 180 degrees */
    for(i = 23; ((i < M) && (i >= 0)); i--)
    {
        for(j = 6; ((j < N) && (j >= 0)); j--)
        {
            fprintf(fout, "%d ", img[i][j]);
        }
    }

    /* for(i = 0; i < M; i++)
    {
        for(j = 0; j < N; j++)
        {
            fprintf(fout, "%d ", img[i][j]);
        }
    } */

    close(fout);
}

int main(int argc, char* argv[])
{
    int i, j;
    int M, N; /* M is the height, N is the width */
    int ** img = 0;
    FILE *file;
    
    file = NULL; /* initialization of pointer */
    
    char c; /* first character of the header */
    int v, max; /* v holds the version */

    char infile[25];
    char outfile[25];

    printf("\nInput File Name(25 characters MAX with .pgm extension) :: ");
    gets(infile);

    printf("\nOutput File Name(25 characters MAX with .pgm extension) :: ");
    gets(outfile);

    file = fopen(infile, "r");

    if(file == NULL)
    {
        printf("File not opened");
        //getch();
        exit(1);
    }

    fscanf(file, "%c%d\n%d %d\n%d", &c, &v, &N, &M, &max);
    fclose(file);

    img = memAlloc(M, N);

    inFile(infile, img, M ,N);
    outFile(outfile, c, v, N, M, max, img);
    system("PAUSE");
    return 0;
}

[/QUOTE]

[Rubberman]

pointer = (int **) calloc(M, sizeof(* int));

should be

pointer = (int **) calloc(M, sizeof(int*));

[ostangel]

pointer = (int **) calloc(M, sizeof(* int));

should be

pointer = (int **) calloc(M, sizeof(int*));

That was still giving me segmentation fault, unfortunately. So I decided to rewrite it will malloc instead of calloc. But now, memory is not being allocated properly in my for loop. It goes all the way till the part where I check if its NULL, and it prints out the error message.

Modified code below:

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

int ** memAlloc(int M, int N)
{
	int i;
	int ** pointer;

	pointer = NULL;

	pointer = malloc(M * sizeof(int **));

	if (pointer == NULL)
	{
		printf("Memory Allocation unsuccessful");
		exit(1);
	}

	for(i = 0; i < N; i++)
	{
		pointer[i] = malloc(N * sizeof(int));

		if(pointer[i] == NULL)
		{	
			printf("Memory Allocation Unsuccessful");
			exit(1);
		}
	}
	return pointer;
}

void inFile(char fn[], int **temp, int M, int N)
{
	int i, j, k;
	char ch[4]; /* header information */

	unsigned int value;
	FILE * fp;
	fp = NULL; /* initialization of pointer */

	fp = fopen(fn, "r");

	if(fp == NULL)
	{
		printf("File not opened");
		exit(1);
	}

	fscanf(fp, "%c%c\n%d %d\n%d", &ch[0], &ch[1], &i, &j, &k);

	for (i = 0; i < M; i++)
	{
		for(j = 0; j < N; j++)
		{
			fscanf(fp, "%d", &value);
			temp[i][j] = value;
		}
	}

	fclose(fp);
}

void outFile(char outfile[], char c, int v, int N, int M, int max, int ** img)
{
	int i, j;
	FILE * fout;
	fout = NULL;

	fout = fopen(outfile, "w");

	fprintf(fout, "%c%d\n", c, v);
	fprintf(fout, "%d %d\n", N, M);
	fprintf(fout, "%d\n", max);

	if(fout == NULL)
	{
		printf("\n Error Opening Output File");
		exit(1);
	}

	for(i = 23; ((i < M) && (i >= 0)); i--)
	{
		for(j = 6; ((j < N) && (j >= 0)); j--)
		{
			fprintf(fout, "%d ", img[i][j]);
		}
	}

	/* for(i = 0; i < M; i++)
	{
		for(j = 0; j < N; j++)
		{
			fprintf(fout, "%d ", img[i][j]);
		}
	} */

	close(fout);
}

int main(int argc, char* argv[])
{
	int i, j;
	int M, N;
	int ** img = 0;
	FILE *file;
	
	file = NULL;
	
	char c; 
	int v, max; 

	char infile[25];
	char outfile[25];

	printf("\nInput File Name(25 characters MAX with .pgm extension) :: ");
	gets(infile);

	printf("\nOutput File Name(25 characters MAX with .pgm extension) :: ");
	gets(outfile);

	file = fopen(infile, "r");

	if(file == NULL)
	{
		printf("File not opened");
		exit(1);
	}

	fscanf(file, "%c%d\n%d %d\n%d", &c, &v, &N, &M, &max);
	fclose(file);

	img = memAlloc(M, N);

	inFile(infile, img, M ,N);
	outFile(outfile, c, v, N, M, max, img);
	system("PAUSE");
	return 0;
}

[Rubberman]

I suppose at this point, we have to ask, what are the values you use for M and N?