c - bsearch 和结构(自定义类型)

Question

我有一个这样的数组:

typedef struct INSTR
{
    char* str;
    int  argc;
} INSTR;
const static INSTR instructions[] = { {"blue",1}, {"green",2} };

然后我尝试执行 bsearch，但我收到了 Segmentation fault 消息:

int comp(const void *a, const void *b)
{
    const INSTR *aa = (INSTR*)a;
    const INSTR *bb = (INSTR*)b; 
    // if I "return 0;" here i get no error.
    return strcmp(aa->str, bb->str);
}

.

char *str = get_string(src_buff, size);
bsearch(str, instructions,
        sizeof(instructions) / sizeof(instructions[0]),
        sizeof(instructions[0]), comp);

Answer 1

comp() 函数不正确。来自 here :

comparator Function that compares two elements. The function shall follow this prototype:

int comparator ( const void * pkey, const void * pelem );

The function must accept two parameters: the first one pointing to the
key object, and the second one to an element of the array, both
type-casted as void*. The function should cast the parameters back to
some data type and compare them.

comp() 的第一个参数是 const char*，而不是 INSTR*。

更改为:

int comp(const void *a, const void *b)
{
    const INSTR *bb = (INSTR*)b; 
    return strcmp((const char*)a, bb->str);
}

或者，将 key 更改为 INSTR* 而不是 const char*。