Segmentation fault 11 (probably in struct) before the main functin even started
I'd like to know where is the mistake in my code. I just started learning C and I just got to pointers and arrays so I have no idea where the mistake is. The problem seems to be in the part where I use struct to create my own data type because none of the debug texts that I've put in show themselves in console when I run the program. I've looked on the internet for an answer but haven t found anything. Any help would be appreciated.
#include <stdio.h>
#include <stdlib.h>
#define MAX_size 2000
typedef struct TMatrix{
int grid[MAX_size][MAX_size];
int sizex;
int sizey;
} TMATRIX;
int readSize(TMATRIX *matrix);
int main(void){
TMATRIX matrix;
printf("DEBUG\n");
if (readSize(&matrix)==1){
printf ("Invalid input.\n");
return 1;
}
printf("%d %d\n", matrix.sizex,matrix.sizey);
return 0;
}
int readSize(TMATRIX *matrix){
printf("DEBUG\n");
if (scanf("%d %d", &matrix->sizex, &matrix->sizey)!=2) return 1;
if (matrix->sizex<1 || matrix->sizey<1) return 1;
return 0;
}
In your TMATRIX structure, you declare an array of integers of 2000x2000.
2000*2000*4 is 16 megabytes. You're using an auto variable approx. that size (that if sizeof(int)==4 but that could be the double if sizeof(int)==8).
So you probably get a stack overflow before you even reach the first instruction, when the compiler-generated code tries to allocate enough stack room for your variable, typical stack sizes are smaller than that.
Fixes:
- increase the stack (linker option)
- use a global variable (move
matrixoutside themainprocedure) - allocate your table using
malloc, and not statically (to keep multidimensional aspect, defineint (*grid)[MAX_size];and make a malloc onMAX_size * sizeof *grid)