Iterating through a std::vector

I have some legacy C which iterates through buffer_1 allocated with some valid memory. buffer_2 is made to point to parts of buffer_1 and the iteration keeps moving random 20 places ahead. Following is the code:

char* buffer_1;
char* buffer_2;
size_t buffer_length;

buffer_length = 2000; // somerandom value

if (buffer_length > 0) {
    buffer_1 = malloc(buffer_length);
    for(buffer_2 = buffer_1; buffer_2 < buffer_1 + buffer_length; buffer_2 += 20) {
        // Some random logic
    }
}

I want to make the above code C++ 11 compliant by declaring buffer_1 and buffer_2 as std::vector<char>s like below.

std::vector<char> buffer_1;
std::vector<char> buffer_2;

Then I think I would need to use an iterator over buffer_1 do something like below?

if (buffer_length > 0) {
    buffer_1.reserve(buffer_length);
    for(std::vector<char>::iterator it = buffer_1.begin(); it != buffer_1.end(); it += 20) {
        buffer_2.data() = *it;
    }
}

is the above way of iterating through a std::vector<char> correct? Does it do exactly what the following for statement does?

for(buffer_2 = buffer_1; buffer_2 < buffer_1 + buffer_length; buffer_2 += 20)