I'm trying to write a code that take two files and compare them with the lcs algoritm. i can't understand why the program give me segmentation fault

Question

//this is extlcs.c

#include <stdio.h>

#include <stdlib.h>

#include "extlcs.h"

typedef struct {

    long long *row;
    long nRow;
    long long *col;
    long nCol;
}ttable;

int Max(int a, int b){

    if(a>b)    return a;
    else    return b;
}

int calcLcs(const long long *row, long Nrow, long Ncol, const long long *col){

    int matrix[Nrow+1][Ncol+1];
    int i,j;
    for(i=0;i<Nrow;i++){
        matrix[i][0]= 0 ;
    }
    for(j=0;j<Ncol;j++){
        matrix[0][j] = 0;
    }
    for(i=1;i<Nrow;i++){
        for(j=1;j<Ncol;j++){
            if(row[i-1]==col[j-1])    matrix[i][j] = matrix[i-1][j-1] + 1;
            else    matrix[i][j] = Max(matrix[i][j-1],matrix[i-1][j]);
        }
    }
    printf("%d", matrix[i][j]);
    return matrix[i][j];
}

int extlcs(char *input1, char *input2, char *output) {


    FILE *prova1 = fopen(input1, "r");
    FILE *prova2 = fopen(input2, "r");

    ttable *table = (ttable*) malloc(sizeof(ttable));

    fseek(prova1,0L,SEEK_END);
    table->nRow = ftell(prova1);
    fseek(prova1, 0L, SEEK_SET);
    printf("%ld\n", table->nRow);
    table->row = 0;
    table->row = (long long*) malloc(table->nRow);


    fseek(prova2,0L,SEEK_END);
    table->nCol = ftell(prova2);
    fseek(prova2, 0L, SEEK_SET);
    printf("%ld\n", table->nCol);
    table->col = 0;
    table->col = (long long*) malloc(table->nCol);


    fread(table->row, sizeof(long long), table->nRow, prova1);
    fread(table->col, sizeof(long long), table->nCol, prova2);


    int res = calcLcs(table->row,table->nRow,table->nCol,table->col);
    printf("%d",res);
    /*
    int vet[40];

    n=fread(vet,sizeof(int),40,prova1);
    for(i=0;i<40;i++)    printf("%d ", vet[i]);
    printf("%d",n);
    fclose(prova2);
    */
    FILE *out = fopen(output, "w");
    printf((const char *) out, "%d\n", res);
    fclose(prova1);
    fclose(prova2);
    fclose(out);
    return res;
}


//this is main.c

#include <stdio.h>

#include "extlcs.h"

int main(int argc, char** argv) {

    if(argc!=4){

        printf("errore");
        return -1;
    }
    extlcs(argv[1],argv[2],argv[3]);
    return 0;
}

Answer 1

I suspect malloc(table->nRow).
It looks too small, only space for nRow bytes, but needs space for nRow long long as far as I can tell.

Similar for malloc(table->nCol).

You probably want to multiply by sizeof(long long).
And better look up some best practices on malloc. (E.g. not repeating types and not casting.)