[英]insertion to map- key is always exist
I have an issue with inserting values to map. 我在插入要映射的值时遇到问题。
#define SIZE 5
#define pair<unsigned char *, int> pair_t
struct myCmp
{
int operator()(const unsigned char arr_1[SIZE], const unsigned char arr_2[SIZE])
{
printf("arr_1: %02x,%02x,%02x,%02x,%02x arr_2: %02x,%02x,%02x,%02x,%02x",
arr_1[0], arr_1[1],arr_1[2],arr_1[3],arr_1[4],
arr_2[0],arr_2[1],arr_2[2],arr_2[3],arr_2[4]);
}
}
void main()
{
map<unsigned char *, int, myCmp> myMap;
map<unsigned char *, int, myCmp>::iterator it;
unsigned char arr[SIZE] = {'\0'};
//---- first insertion ----//
arr[0] 0xa;
pait_t data_1(arr,1);
pair< map<unsigned char *, int, myCmp>::iterator> ret_1 = myMap.insert(data_1);
if(ret_1.second)
printf("added one");
else
printf("already exist one");
//---- second insertion ----//
arr[1] 0xb;
pait_t data_2(arr,2);
pair< map<unsigned char *, int, myCmp>::iterator> ret_2 = myMap.insert(data_2);
if(ret_2.second)
printf("added two");
else
printf("already exist two");
}
the first insertion is ok, myCmp
is not activated yet and I get added one
第一次插入没问题,
myCmp
尚未激活,我added one
the problem is with the second insertion, it seems that myCmp
gets the same two arrays and always return 0 (equal)- it prints arr_1: ab arr_2: ab
so the ret_2.second
is false (key is already exist) and prints already exist two
. 问题是第二次插入,看来
myCmp
会得到相同的两个数组,并且总是返回0(等于)-它会打印arr_1: ab arr_2: ab
所以ret_2.second
为false(键已经存在)并且打印already exist two
。
I tried to change the value of arr, but it doesn`t have any affect. 我试图更改arr的值,但是它没有任何影响。
the strange part is when I tried to do the same but instead of char *
I used string
(changed the all the signatures of course..), the myCmp
function got two different values. 奇怪的是,当我尝试执行相同的操作但不使用
char *
我使用了string
(当然更改了所有签名。), myCmp
函数得到了两个不同的值。
I can`t use string as key.. 我不能使用字符串作为键。
I don't know why it behaves like this and myCmp
gets two identical values. 我不知道为什么它会这样,并且
myCmp
获得两个相同的值。
I will be happy for guidance on that matter. 我很乐意为您提供指导。
You're giving the arr address that is the same in both cases. 您提供的arr地址在两种情况下都相同。 Try using a
std::string
. 尝试使用
std::string
。
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