I'm trying to build an edge detection program using the code below. I have faced a variety of problems though, that I don't know how to solve.
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#define xrows 700
#define ycolumns 1244
int Gradient[xrows][ycolumns];
int Image_input[xrows][ycolumns];
int G_x[xrows][ycolumns];
int G_y[xrows][ycolumns];
int main() {
FILE *fw = fopen("sobel_outt.txt", "w");
FILE *fr = fopen("ny.txt", "r");
int x, y, row, column, num;
int i = 0;
int XLENGTH = 700;
int YLENGTH = 1244;
for (row = 0; row < XLENGTH; row ) {
for (column = 0; column < YLENGTH; column ) {
fscanf(fr, "%d " ",", &num);
Image_input[row][column] = num;
}
}
fclose(fr);
for (x = 0; x < XLENGTH; x = 3) {
i ;
for (y = 0; y < YLENGTH; y = 3) {
if ((x == 0) || (x == XLENGTH - 1) || (y == 0) || (y == YLENGTH - 1)) {
G_x[x][y] = G_y[x][y] = Gradient[x][y] = 0;
} else {
G_x[x][y] = Image_input[x 1][y - 1]
2 * Image_input[x 1][y]
Image_input[x 1][y 1]
- Image_input[x - 1][y - 1]
- 2 * Image_input[x - 1][y]
- Image_input[x - 1][y 1];
G_y[x][y] = Image_input[x - 1][y 1]
2 * Image_input[x][y 1]
Image_input[x 1][y 1]
- Image_input[x - 1][y - 1]
- 2 * Image_input[x][y - 1]
- Image_input[x 1][y - 1];
Gradient[x][y] = (abs(G_x[x][y]) abs(G_y[x][y]));
if (Gradient[x][y] > 255) {
Gradient[x][y] = 255;
}
}
fprintf(fw, "%d,\n", Gradient[x][y]);
}
}
printf("i= %d", i);
fclose(fw);
return 0;
}
The program seems to execute fine when run in the devcpp IDE and all of the matrices are declared as global variables. Whenever I declare them inside the main function, the program crashes.
I tried to run the program using Visual Studio, but I faced a couple more problems. I got some error messages stating that fscanf
is ignored and fprintf
is unsafe.
Last but not least I got another error, stating that I used up all of the stack memory available.
Any suggestions would be welcomed .
EDIT: Many of you suggested that I caused a stack overflow. I will try to use the heap memory as an alternative. My second problem still remains though.
CodePudding user response:
Defining your matrices as local variables with automatic storage uses close to 14MB of stack space. This can definitely cause a stack overflow on many platforms. Allocating the data from the heap is recommended.
Microsoft's Visual C compiler is configured to complain about fscanf
and fprintf
and advocates using fscanf_s
and fprintf_s
instead. They managed to get this and other functions included the C Standard (Annex K) but the API was changed in subtle ways for consistency (using size_t
instead of UINT
for array lengths) and Microsoft did not change their version. This difference was unimportant for 32-bit targets but types size_t
and unsigned
now differ on most 64-bit platforms.
Using fscanf_s()
is therefore not recommended for portable programs. You can disable the compiler warning by adding #define _CRT_SECURE_NO_WARNINGS
before including <stdio.h>
.
Note however that you should not ignore the return value of fscanf()
to detect invalid or missing data: if the conversion fails the destination variable is unchanged, leading to incorrect results or even undefined behavior.
Here is a modified version allocating the matrices from the heap:
#ifdef _MSC_VER
#define _CRT_SECURE_NO_WARNINGS // disable warnings in fscanf
#endif
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ROWS 700
#define COLS 1244
int main() {
int (*Gradient)[COLS] = calloc(sizeof(*Gradient), ROWS);
int (*Image_input)[COLS] = calloc(sizeof(*Image_input), ROWS);
int (*G_x)[COLS] = calloc(sizeof(*G_x), ROWS);
int (*G_y)[COLS] = calloc(sizeof(*G_y), ROWS);
if (!Gradient || !Image_input || !G_x || !G_y) {
fprintf(stderr, "cannot allocate memory\n");
return 1;
}
FILE *fr = fopen("ny.txt", "r");
if (fr == NULL) {
fprintf(stderr, "cannot open ny.txt: %s\n", strerror(errno));
return 1;
}
FILE *fw = fopen("sobel_outt.txt", "w");
if (fw == NULL) {
fprintf(stderr, "cannot open sobel_outt.txt: %s\n",
strerror(errno));
return 1;
}
int x, y, row, column, num;
int i = 0;
int XLENGTH = ROWS;
int YLENGTH = COLS;
for (row = 0; row < XLENGTH; row ) {
for (column = 0; column < YLENGTH; column ) {
if (fscanf(fr, "%d ,", &num) != 1) {
fprintf(stderr, "cannot read value for Image_input[%d][%d]\n",
row, column);
return 1;
}
Image_input[row][column] = num;
}
}
fclose(fr);
for (x = 0; x < XLENGTH; x = 3) {
i ;
for (y = 0; y < YLENGTH; y = 3) {
if (x == 0 || x == XLENGTH - 1 || y == 0 || y == YLENGTH - 1) {
G_x[x][y] = G_y[x][y] = Gradient[x][y] = 0;
} else {
G_x[x][y] = Image_input[x 1][y - 1]
2 * Image_input[x 1][y]
Image_input[x 1][y 1]
- Image_input[x - 1][y - 1]
- 2 * Image_input[x - 1][y]
- Image_input[x - 1][y 1];
G_y[x][y] = Image_input[x - 1][y 1]
2 * Image_input[x][y 1]
Image_input[x 1][y 1]
- Image_input[x - 1][y - 1]
- 2 * Image_input[x][y - 1]
- Image_input[x 1][y - 1];
Gradient[x][y] = abs(G_x[x][y]) abs(G_y[x][y]);
if (Gradient[x][y] > 255) {
Gradient[x][y] = 255;
}
}
fprintf(fw, "%d,\n", Gradient[x][y]);
}
}
fclose(fw);
printf("i= %d\n", i);
free(Gradient);
free(Image_input);
free(G_x);
free(G_y);
return 0;
}
Note that the final value of i
should always be XLENGTH
.
Here is an alternative using a single structure for all data, easier to handle than allocated 2D matrices:
#ifdef _MSC_VER
#define _CRT_SECURE_NO_WARNINGS
#endif
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ROWS 700
#define COLS 1244
struct sobel {
int Gradient[ROWS][COLS];
int Image_input[ROWS][COLS];
int G_x[ROWS][COLS];
int G_y[ROWS][COLS];
};
int main() {
struct sobel *data = (struct sobel *)calloc(sizeof(*data), 1);
if (!data) {
fprintf(stderr, "cannot allocate memory\n");
return 1;
}
FILE *fr = fopen("ny.txt", "r");
if (fr == NULL) {
fprintf(stderr, "cannot open ny.txt: %s\n", strerror(errno));
return 1;
}
FILE *fw = fopen("sobel_outt.txt", "w");
if (fw == NULL) {
fprintf(stderr, "cannot open sobel_outt.txt: %s\n", strerror(errno));
return 1;
}
int x, y, row, column, num;
int i = 0;
int XLENGTH = ROWS;
int YLENGTH = COLS;
for (row = 0; row < XLENGTH; row ) {
for (column = 0; column < YLENGTH; column ) {
if (fscanf(fr, "%d " ",", &num) != 1) {
fprintf(stderr, "cannot read value for Image_input[%d][%d]\n", row, column);
return 1;
}
data->Image_input[row][column] = num;
}
}
fclose(fr);
for (x = 0; x < XLENGTH; x = 3) {
i ;
for (y = 0; y < YLENGTH; y = 3) {
if (x == 0 || x == XLENGTH - 1 || y == 0 || y == YLENGTH - 1) {
data->G_x[x][y] = data->G_y[x][y] = data->Gradient[x][y] = 0;
} else {
data->G_x[x][y] = data->Image_input[x 1][y - 1]
2 * data->Image_input[x 1][y]
data->Image_input[x 1][y 1]
- data->Image_input[x - 1][y - 1]
- 2 * data->Image_input[x - 1][y]
- data->Image_input[x - 1][y 1];
data->G_y[x][y] = data->Image_input[x - 1][y 1]
2 * data->Image_input[x][y 1]
data->Image_input[x 1][y 1]
- data->Image_input[x - 1][y - 1]
- 2 * data->Image_input[x][y - 1]
- data->Image_input[x 1][y - 1];
data->Gradient[x][y] = abs(data->G_x[x][y]) abs(data->G_y[x][y]);
if (data->Gradient[x][y] > 255) {
data->Gradient[x][y] = 255;
}
}
fprintf(fw, "%d,\n", data->Gradient[x][y]);
}
}
fclose(fw);
printf("i= %d\n", i);
free(data);
return 0;
}