Code to print the Longest Common Substring in C - c

Question

I wrote the code to print the longest common substring in C language perogramming. When I run the code it says "segmentation core dumped". Please help me I want to know the problem because it was working at first and then it suddenly gave this error.
#include<string.h>
#include <stdio.h>
#define new_max(x,y) (((x) >= (y)) ? (x) : (y))
#define new_min(x,y) (((x) <= (y)) ? (x) : (y))
void LCSubStr(char *X, char *Y, int m, int n)
{
int LCSuff[m+1][n+1];
int result = 0;
int end;
for (int i=0; i<=m; i++)
{
for (int j=0; j<=n; j++)
{
if (i == 0 || j == 0)
LCSuff[i][j] = 0;
else if (X[i-1] == Y[j-1])
{
LCSuff[i][j] = LCSuff[i-1][j-1] + 1;
result = new_max(result, LCSuff[i][j]);
end = i - 1;
}
else{
LCSuff[i][j] = 0;
}
}
}
if(result = 0){
printf("No common substring");
}else{
char subbuff[5];
memcpy(subbuff, &X[end - result + 1], result);
subbuff[result] = '\0';
printf("%s",subbuff);
}
}
int main()
{
char X[] = "Sandile";
char Y[] = "andile";
int m = strlen(X);
int n = strlen(Y);
LCSubStr(X, Y, m, n);
return 0;
}

Answer 1

Instead of copying to a fixed length string, you can directly specify the length with printf.
char subbuff[5];
memcpy(subbuff, &X[end - result + 1], result);
subbuff[result] = '\0';
printf("%s",subbuff);
Instead, try:
printf("%.*s",result, &X[end-result+1])
(The '.*s' syntax uses a limit in the parameter list - the result or length of match in this case)
Also, be careful of =.
if(result = 0){
printf("No common substring");
It's traditional to reverse comparisons in C to avoid this typo.
if (0 == result) {
printf("No common substring");

Answer 2

I believe, in this statement
if(result = 0){
= is typo and you mean == i.e. if (result == 0) ....
Your program is accessing an array beyond its size, which is an undefined behaviour:
char subbuff[5];
memcpy(subbuff, &X[end - result + 1], result);
the size of subbuff is 5 and the size of longest common substring, for the given input (X = "Sandile" and Y = "andile"), is 6. The memcpy, while copying the bytes, end up accessing the array subbuff beyond its size. You need a destination buffer of minimum size 7 (6 characters + 1 null terminating character) to hold the common substring (for the given input).
As #Halt State suggested, you can print the specific number of characters of input string, starting from a position in the string:
if(result = 0){
printf("No common substring");
}else{
printf("%.*s",result, &X[end-result+1]);
}
Alternatively, you can allocate the memory dynamically and copy the longest common string in that memory. In this case, instead of printing longest common string in LCSubStr() function, you may return it from LCSubStr() function which enables the calling function to process something based on the returned string, if required. It's implementation:
....
#include <stdlib.h> // for malloc
....
char * LCSubStr (char *X, char *Y, int m, int n) {
....
....
char * subbuff = NULL;
if (result > 0) {
subbuff = malloc (result + 1);
if (subbuff == NULL) {
fprintf (stderr, "Failed to allocate memory\n");
exit (EXIT_FAILURE);
}
memcpy (subbuff, &X[end - result + 1], result);
subbuff[result] = '\0';
}
return subbuff;
}
// In the calling function
int main (void) {
....
....
char * lcs = LCSubStr (X, Y, m, n);
if (lcs != NULL) {
printf ("%s\n", lcs);
// Once the calling function done with returned buffer, free it
free (lcs);
} else {
printf ("No common substring\n");
}
return 0;
}