Question

我的布尔函数在找到“ needle”时应返回true，但即使返回false并打印出“找不到针” 我尝试使用GDB进行调试，事实证明它实际上返回true，但之后又返回false，而在满足条件后不会中断??

这是我的代码：

int FindMidPoint(int array[],int size)
{
int i = size / 2;
int Midpoint = array[i];
return Midpoint;
}


bool search(int value, int array[], int n)
{
// TODO: implement a searching algorithm
if ( n <= 0 )
return false; 

int Midpoint = FindMidPoint(array,n);
int mid = n / 2;
int x = round(mid);
int *firsthalf = malloc((x) * sizeof(int));
int *secondhalf = malloc((x) * sizeof(int));
memcpy(firsthalf,array, x * sizeof(int));
memcpy(secondhalf,array + x, x * sizeof(int));

if (value == Midpoint)
    {
    return true;
    }
else if (value > Midpoint)
        {
        search (value,secondhalf,mid);

        }
else if (value < Midpoint)
        {
        search(value,firsthalf,mid);    
        }
return false;
}

这是GDB给我的：

Starting program: /root/cs50/pset3/hacker3/find/find 10

 haystack[0] = 10

haystack[1] = 12

haystack[2] = 14

haystack[3] = 6

haystack[4] = 8


haystack[5] = 20


haystack[6] = 200


haystack[7] = 2000


haystack[8] = 202


haystack[9] = 


 6 


 8 


 10 


 12 


 14 


 20 


 200 


 202 


 2000 


Breakpoint 1, search (value=10, array=0x7ffffffbe100, n=9) at 
helpers.c:32

32      if ( n <= 0 )

(gdb) n

35      int Midpoint = FindMidPoint(array,n);

(gdb) n

36      int mid = n / 2;

(gdb) n

37      int x = round(mid);

(gdb) n

38      int *firsthalf = malloc((x) * sizeof(int));

(gdb) n

39      int *secondhalf = malloc((x) * sizeof(int));

(gdb) n

40      memcpy(firsthalf,array, x * sizeof(int));

(gdb) n

41      memcpy(secondhalf,array + x, x * sizeof(int));

(gdb) n

43      if (value < Midpoint)

(gdb) n

45          search(value,firsthalf,mid);    

(gdb) n


Breakpoint 1, search (value=10, array=0x405850, n=4) at helpers.c:32

32      if ( n <= 0 )

(gdb) n

35      int Midpoint = FindMidPoint(array,n);

(gdb) n

36      int mid = n / 2;

(gdb) n

37      int x = round(mid);

(gdb) n

38      int *firsthalf = malloc((x) * sizeof(int));

(gdb) n

39      int *secondhalf = malloc((x) * sizeof(int));

(gdb) n

40      memcpy(firsthalf,array, x * sizeof(int));

(gdb) n

41      memcpy(secondhalf,array + x, x * sizeof(int));

(gdb) n

43      if (value < Midpoint)

(gdb) info locals

Midpoint = 10

mid = 2

x = 2

firsthalf = 0x405890

secondhalf = 0x4058b0

(gdb) n

47      else if (value > Midpoint)

(gdb) info locals

Midpoint = 10

mid = 2

x = 2

firsthalf = 0x405890

secondhalf = 0x4058b0

(gdb) n

52      else if (value == Midpoint)

(gdb) n

54          return true;

(gdb) n

64  }

(gdb) n

search (value=10, array=0x7ffffffbe100, n=9) at helpers.c:46

46          }

(gdb) n

62      return false;

(gdb) n

64  }

(gdb) 

main (argc=2, argv=0x7fffffffe238) at find.c:69

69          printf("\nDidn't find needle in haystack.\n\n");

(gdb) 


Didn't find needle in haystack.


70          return 1;

我不知道我的代码有什么问题，或者我不了解布尔函数，请帮忙！

Answer 1

只有在第一次调用时满足以下条件，search函数才会返回true：

：

value == Midpoint

进行所有递归调用，但其结果被忽略，并且始终返回false：

else if (value > Midpoint)
{
    search(value,secondhalf,mid);
}
else if (value < Midpoint)
{
    search(value,firsthalf,mid);    
}
return false;

您需要从递归返回结果：

else if (value > Midpoint)
{
    return search(value,secondhalf,mid);
}
else if (value < Midpoint)
{
    return search(value,firsthalf,mid);    
}
return false;

我的布尔函数返回true然后为false？

1 个答案: