分段错误：倒车时的字符串

Question

#include<stdio.h>
#include<string.h>
void reverseMe(char *,int,int);
int main()
{
  char str[]="cycle";
  int len=strlen(str);
  reverseMe(str,0,len-1);
  return 0;
}

void reverseMe(char *x,int begin,int end)
{
  char c;
  c=*(x+begin);
  *(x+begin)=*(x+end);
  *(x+end)=c;

  reverseMe(x,++begin,--end);
}

Why do I get segmentation error? What is the error I have made?

Answer 1

Huh?

You never check against the limits of the string, reverseMe() does infinite recursion. Of course it's going to give your fireworks.

You should have something like

if(begin < end)
{
  const char c = x[begin];
  x[begin] = x[end];
  x[end] = c;
  reverseMe(x, begin + 1, end - 1);
}

inside reverseme() . Also note that array indexing is clearer than pointer arithmetic, in many cases.

Answer 2

Your function is invalid because there is no condition to exit the function (recursion).

Try the following

void reverseMe( char *s, int begin, int end )
{
   if ( begin < end )
   {
      char c =  s[begin];
      s[begin] = s[end];
      s[end] = c;
      reverseMe( s, begin + 1, end - 1 );
   }
}

Also as this function deals with strings then I would define it the following way

char * reverseMe( char *s, int begin, int end )
{
   if ( begin < end )
   {
      char c =  s[begin];
      s[begin] = s[end];
      s[end] = c;
      return reverseMe( s, begin + 1, end - 1 );
   }

   return s;
}

In this case you could use it the following way

char str[] = "cycle";
printf( "%s\n", reverseMe( str, 0, strlen( str ) - 1 ) );