如何以十六进制修改地址 ip？

Question

I am displaying adress ip of some network nodes with using a network simulator, But I don't have the expected result.

I display ip adress with using this function:

void print_hex_src_adress(uint8_t *s, size_t len)
{
    printf("  ID=");
    for(int i=0; i< len; i++) {
        printf("%02x", s[i]);
    }
}

Then in order to display the adress I put:

open_addr_t * myaddress;
myaddress = idmanager_getMyID(ADDR_64B);
print_hex_src_adress(myadress, 16);

But the result that I have is not the expected result:

  ID=02141592cc0000000400000093947ae2

the expected result is:

  ID=02141592cc0000000400000000000000

Answer 1

idmanager_getMyID returns a pointer to a union of type open_addr_t . A union is an object big enough to hold any of the fields it could contain. That does not mean that all the data in it will be initialized. You are requesting ADDR_64B , which means that only the first 64 bits, or 8 bytes, of the union are likely to be initialized via the addr_64b field.

What is effectively happening is that you are invoking undefined behavior, trying to print bytes that contain trash values. The good news is that you won't run into memory that you aren't allowed to use because the union is at least 16 bytes. You are expecting the trash to be zeros, but instead are getting actual trash. You have two options:

1. Print the bytes you actually requested:

    print_hex_src_adress(myadress.addr_64b, sizeof(myadress.addr_64b));

   Using sizeof for something like this is a good habit to have. Structures and unions can change between versions, but writing it like this makes your code mode robust against such changes.

2. Request the bytes you actually want:

    myaddress = idmanager_getMyID(ADDR_128B);

   Still refer to the correct field when you print, and don't hard-code the size so much:

    print_hex_src_adress(myadress.addr_128b, sizeof(myadress.addr_128b));