Conversion error when passing vector of type uint8_t to std::fill() in C-CodePudding

I am using the below code snippet to pass vector of type "uint8_t" to std::fill()

size_t actual_size = 10;
std::vector<uint8_t> response;
std::fill(response.begin(), response.end()   actual_size, 0);

But i am getting the below warnings.

 message : see reference to function template instantiation 'void std::fill<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>,int>(const _FwdIt,const _FwdIt,const int &)' being compiled
        with
        [
            _Ty=uint8_t,
            _FwdIt=std::_Vector_iterator<std::_Vector_val<std::_Simple_types<uint8_t>>>
        ]

 warning C4244: '=': conversion from 'const _Ty' to 'unsigned char', possible loss of data
        with
        [
            _Ty=int
        ]

How to resolve this warning.

CodePudding user response：

The reason you are getting the warning is because when filling 0(an int) to a vector<uint8_t>, you are implicitly converting an int to an uint8_t, which can potentially have data loss if the original int is not in the valid range of uint8_t.

To solve it, you can either create a uint8_t directly, or manually cast the int to uint8_t.

Also, when you do:

std::fill(vec.begin(), vec.end()   some_size, some_value)

You are literally filling elements pass the end iterator, without resizing the vector, which is likely not what you wanted.

Instead, you should use fill_n to specify the number of element to fill, and use back_inserter to push it to the vector:

std::fill_n(std::back_inserter(vec), some_size, some_value);

Or you can simply initialize the vector with the appropriate data filled:

std::vector<std::uint8_t> vec(some_size, some_value);

Or even zero initialize them, since you were going to assign them to 0s:

std::vector<std::uint8_t> vec(some_size);