Question

Please see the code snippet below :

#include <iostream>
using namespace std;

int main()
{
uint32_t len, x;
char abc[] = "12345678";
uint8_t *ptr = (uint8_t *)abc;
copy(ptr, ptr + 4, reinterpret_cast<uint32_t*>(&len));
cout << " len: " << len << endl;
} 

The output is 49! I would want the output to be 1234. Am I missing something

Answer 1

Your target is a “container” of length 1 (namely, a single object, len).

You are copying four subsequent byte values into this container, which of course fails – in particular, it causes an overflow since the target only has space for a single element.

Other errors in your code (not an exhaustive list):

• You are confusing character codes and their string representation
• You are performing redundant casts

The first point in particular is relevant since what you actually want to do is parse the number encoded in the first four characters of the string as a decimal number. But what you actually do is copy its character codes.

To parse a number in C++, use as std::stringstream or, since C++11, std::stoi