总线10错误与递归调用

Question

So I'm having trouble with this recursive function call... I am trying to program a function that will check to see if every string in my struct follows alphabetical order, and if it is true, it will return 1, if not, it will return 0.

I keep getting a bus 10 error, and I have tried putting print statements/cannot find where my error is. Can anyone help? Thank you.

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

typedef struct string_list string_list;
struct string_list {
  char *val;
  string_list *next;
};

int sl_sorted_asc(string_list *ss) {

 int  string_c = strcmp(ss->val, ss->next->val);
 if (string_c >= 0) {
   if (ss->next != NULL) {
   sl_sorted_asc(ss->next);
   }
   else {
     return 1;
   }
 }
 else  {
   return 0;
 }
 return 1;
}

int main() {

  string_list hi;
  hi.val = "Leeho";
  hi.next->val = "Ferris";
  hi.next->next->val = "Donny";

printf("%d\n", sl_sorted_asc(&hi));

}

Answer 1

It may be because in this line of your sl_sorted_asc function

 int  string_c = strcmp(ss->val, ss->next->val);

You are not first checking to see if ss->next is null or not.

Answer 2

(compulsory link to http://ericlippert.com/2014/03/05/how-to-debug-small-programs/ )

To figure out problems like this, there's a program called valgrind which is simply invaluable (as in, if your OS doesn't support it, get a virtual machine NOW!); eg in this case it reports ==3637== Use of uninitialised value of size 8 ==3637== at 0x4005BE: main (bus10.c:33)

Line 33 is "hi.next->val = ..."; the problem (in this line - is it the only place?) is that, well, you never did "hi.next = ...", so hi.next points to... what? Basically, anything - the moment the stack is grown to make room for the hi variable, hi.next will take whatever bits were in there, meaning it can point to just about anything (including itself, memory addresses that do not exist- you name it).

TLDR: never, ever use a variable you did not initialize (unless you want expert C programmers to lecture you on "undefined behavior" & friends)

Answer 3

the code is referencing memory that is not allocated

for instance in the following lines:

// allocates one instance of the struct on the stack
string_list hi;    

// sets the 'val' field of the instance of the struct on the stack
hi.val = "Leeho";    

// follows a non-initialized pointer, 
// in the instance of the struct on the stack,
// to a non allocated instance of the struct
// then writes on that non allocated instance of the struct
// I.E. writes to random memory address
hi.next->val = "Ferris";   

// follows a non-initialized pointer
// contained in a non allocated instance of the struct
// to a non allocated instance of the struct
// then writes on that non allocated instance of the struct  
// I.E. follows random values in memory 
//      to some random location in memory
//      then writes on an offset to that random location           
hi.next->next->val = "Donny";