After writing a program to reverse a string, I am having trouble understanding why I got a seg fault while trying to reverse the string. I have listed my program below.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void reverse(char *);
int main() {
char *str = calloc(1,'\0');
strcpy(str,"mystring0123456789");
reverse(str);
printf("Reverse String is: %s\n",str);
return 0;
}
void reverse(char *string) {
char ch, *start, *end;
int c=0;
int length = strlen(string);
start = string;
end = string;
while (c < length-1){
end++;
c++;
}
c=0;
while(c < length/2){
ch = *end;
*end = *start;
*start = ch;
start++;
end--;
c++;
}
}
1st Question:
Even though I have allocated only 1 byte of memory to the char pointer
str (calloc(1,'\0')), and I copied a 18 bytes string mystring0123456789 into it, and it didn't throw any error and the program worked fine without any SEGFAULT.
Why did my program not throw an error? Ideally it should throw some error as it don't have any memory to store that big string. Can someone throw light on this?
The program ran perfectly and gives me output Reverse String is: 9876543210gnirtsym.
2nd Question:
If the replace the statement
strcpy(str,"mystring0123456789");
with
str="mystring0123456789\0";
the program gives segmentation fault even though I have allocated enough memory for str (malloc(100)).
Why the program throwing segmentation fault?
