error: cast from ‘uint8_t* {aka unsigned char*}’ to ‘unsigned int’ loses precision [-fpermissive]

Question

I want to print addresses of member elements of a structure variable. When i try to compile this program it gives me error (error: cast from ‘uint8_t* {aka unsigned char*}’ to ‘unsigned int’ loses precision [-fpermissive]).I am using https://www.onlinegdb.com/online_c++_compiler. Note: i am using unsigned(ptr) otherwise it gives some ASCII characters.(If i defined pointer variable uint16_t ptr; ptr = (uint16_t)&data; Then it also works but not for uint8_t.)

#include <iostream>
using namespace std;

struct DataSet
{
    char  data1;
    int   data2;
    char  data3;
    short data4;
};

int main(void)
{
    struct DataSet data;

    data.data1  = 0x11;
    data.data2  = 0XFFFFEEEE;
    data.data3  = 0x22;
    data.data4  = 0xABCD;

    uint8_t *ptr;
    ptr = (uint8_t*)&data;

    uint32_t totalSize = sizeof(struct DataSet);
    
    for(uint32_t i = 0 ; i < totalSize ; i++)
    {
        cout<<hex<<unsigned(ptr)<<endl;  // Here i get error.So how can i print these addresses using uint8_t.
        ptr++;
    }
}

Answer 1

Using the online-compiler you provided and changing this line

cout<<hex<<unsigned(ptr)<<endl;

to

cout << hex << (uintptr_t) ptr << std::endl;

prints the addresses.

When checking the size of these datatypes using:

std::cout << "sizeof(uintptr_t) = " << sizeof(uintptr_t) << std::endl;
std::cout << "sizeof(unsigned int) = " << sizeof(uint8_t*) << std::endl;
std::cout << "sizeof(unsigned int) = " << sizeof(unsigned int) << std::endl;

the output is:

sizeof(uintptr_t) = 8
sizeof(uint8_t*) = 8                                                                                                                                                                                                                                                                                                                     
sizeof(unsigned int) = 4   

The pointer-size is 8 byte while your unsigned int type has only a size of 4 bytes. That's why this error appears. The upper 8 byte are cut off and the address wouldn't be correct.