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*)’

short answer: you shouldn't do it. user char array instead. — user3528438
– user3528438, Commented Feb 10, 2016 at 17:40
@YSC: Thanks , im using c++, so please write the cast line in above case? — Ragav
– Ragav, Commented Feb 10, 2016 at 17:43
I know what you need to do, I don't know why you want to do it. — erip
– erip, Commented Feb 10, 2016 at 17:45

Cheers and hth. - Alf · Accepted Answer · 2018-03-07 14:24:37Z

15

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.

edited Mar 7, 2018 at 14:24

answered Feb 10, 2016 at 17:43

Cheers and hth. - Alf

146k15 gold badges218 silver badges342 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Simon Kraemer Over a year ago

return is missing.

Simon Kraemer Over a year ago

-.- I was mislead by the trailing return type... and by my lazyness: not to double check...

Ragav Over a year ago

@ Cheers and hth. - Alf : Thanks a Lot !!

Cheers and hth. - Alf Over a year ago

Just looking at this I realized that with a C++ implementation where std::string has raw pointers as iterators (unlikely but permitted), the unqualified call to copy would not invoke Argument Dependent Lookup and it would not be found. Fixed by adding namespace qualification.

Jodo · Accepted Answer · 2020-01-10 18:59:32Z

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());
}

answered Jan 10, 2020 at 18:59

Jodo

4,7938 gold badges41 silver badges51 bronze badges

Collectives™ on Stack Overflow

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

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related