How to copy every 16 bytes of data from a string? - c++

Question

I have to copy data into sets of 16 bytes. How do i do it with an easy way?
I've come up with the below algorithm but how do i know if the null terminator has been added? thanks! :)
std::string input
//get message to send to client
std::cout << "Enter message to send (type /q to quit) : ";
getline(std::cin, input);
input += '\n';
const char *data = input.c_str();
len = strlen(data)+1;
int max_len =17;
//split msg into 16 bytes
for(int i = 0; i < len ; i+=max_len)
{
char tempStr[max_len];
//get next 16 bytes of msg and store
for(int j = 0; j < max_len ; j++)
{
tempStr[j] = data[j+i];
}//end of for loop
//Do some stuff to tempStr
}

Answer 1

In your code, the string terminator is not added. You also skip one character between the copies (since you have max_len as 17 while you only copy 16characters).
I would propose a solution using the standard library instead:
std::string::const_iterator pos = input.begin();
while (pos < input.end())
{
// Create a temporary string containing 17 "null" characters
char tmp[17] = {'\0' };
// Make sure we co no copy beyond the end
std::string::const_iterator end =
(pos + 16 < input.end() ? pos + 16 : input.end());
// Do the actual copying
std::copy(pos, end, tmp);
// Advance position
pos += 16;
// Use the string in 'tmp', it is properly terminated
}

Answer 2

const char* data = input.c_str();
int len = input.size(); // don't add 1
for (int i=0; i<len; i+=16)
{
char tempStr[17];
tempStr[16] = 0;
strncpy(tempStr, data + i, 16);
// Do some stuff to tempStr
}
Depending upon what you actually do with tempStr, there might be a solution that involves no copying at all.
for (int i=0; i<len; i+=16)
{
llvm::StringRef sref(data + i, data + std::min(i+16,len));
// use sref
}
llvm::StringRef