#include <stdio.h>
#include <stdlib.h>

void reverseString( char *str );
int main()
{
char *str = "abcdefg";
reverseString(str);
printf("Reverse Result: %s\n", str);
return 0;
}

void reverseString( char *str2 )
{
char *str = str2;
char *last = str;

while(*last != '\0')
{
last++;
}
last--;

while(str < last)
{
char ch = *str;
*(str++) = *last;
*(last--) = ch;
}
}

above is my program, it is the exercise 2 chapter 6, on the book of pointer on c,i dont understand why it has the following error:

Program received signal SIGSEGV, Segmentation fault.
In ?? () ()

Please help me thanks