分段故障（核心转储）分配内存？

Question

Im getting the error "Segmentation fault (core dumped)" when I run this program. I am new to c programming so its probably something stupid but i cant figure it out.

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

void swap(char *x, char *y){
    char temp = *x;
    *x=*y;
    *y=temp;
}

char** getPermutations(char *string){
    int length = strlen(string);
    int startIndex = 0;
    int endIndex = length - 1;

    if(startIndex == endIndex){
            printf("%s\n", string);
    }else{
            for(int j = startIndex; j<=endIndex; j++){
                    swap((string + startIndex),(string + j));
                    getPermutations(string);
                    swap((string+startIndex),(string+j));
            }  
    }    
}

int main(int argc, char *argv[]){
     if(argc>2){
            printf("\nToo Many arguments\n");
            exit(0);
    }else{
            printf("%s",argv[1]);
            char * str = malloc(strlen(argv[1]) + 1);
            strcpy(str,argv[1]);
            getPermutations(str);
    }
}

Answer 1

Your issue is that getPermutations calls itself endlessly. You need to pass something extra to it so it can know when to stop. As is, it just calls itself over and over until you have a stack overflow.

Also, you have getPermutations setup to return a char** , but then you never return anything. So that's odd too.

Answer 2

My suggestions:

1. Change the return type of the function to void since it does not return anything.

2. Change the name of the function to printPermutations since it just prints the permutations.

3. Provide a way to end the recursion. Pass startIndex as an argument.

4. Pass the length of the string so you don't compute it every time the function is called recursively.

5. Change the comparison operator to >= to account for zero length strings.

---

void printPermutations(char *string, int startIndex, int length){
   int endIndex = length - 1;

   if(startIndex >= endIndex){
      printf("%s\n", string);
   }else{
      for(int j = startIndex; j<=endIndex; j++){
         swap((string + startIndex),(string + j));
         printPermutations(string, startIndex+1, length);
         swap((string+startIndex),(string+j));
      }  
   }    
}

and call it with:

printPermutations(str, 0, strlen(str));