How to copy a std::string to unsigned char array?

Question

How to copy a std::string (sample) to unsigned char array (trap)?

int main() {
    unsigned char trap[256];
    std::string sample = ".1.3.6.1.4";
    strcpy(trap,sample.c_str());
    std::cout << trap << std::endl;
}

Above code throws error:

time.cpp: In function ‘int main()’:
time.cpp:20: error: invalid conversion from ‘unsigned char*’ to ‘char*’
time.cpp:20: error:   initializing argument 1 of ‘char* strcpy(char*, const char*)’

Answer 1

Here's one way:

#include <algorithm>
#include <iostream>

auto main() -> int
{
    unsigned char trap[256];
    std::string sample = ".1.3.6.1.4";
    std::copy( sample.begin(), sample.end(), trap );
    trap[sample.length()] = 0;
    std::cout << trap << std::endl;
}

It can be a good idea to additionally check whether the buffer is sufficiently large.

Answer 2

Using reinterpret_cast would also be possible:

int main() {
    std::string sample = ".1.3.6.1.4";
    auto uCharArr = reinterpret_cast<unsigned char*>(sample.c_str());
}