Add a newline every set amount of letters in std::string - c++

Question

I'm working with a few long strings inside a C++ program (up to 65535 letters).
What am looking for is a way to add a new line every set amount of letters with an function like this:
addNewLinesToString(std::string* string, u8 lettersBetween newline);
Which would work like this:
string test = "Testing1234567";
addNewLinesToString(&test, 7); //test == "Testing\n1234567\n"
I have yet to find such a function that only used the standard class library (C and/or C++)
If somebody has a simple solution for this would be great :)
Thanks.

Answer 1

You can use string::insert for this purpose.
addNewLinesToString(std::string& str, int sep)
{
for (int i = 0; i < str.size(); i += sep)
str.insert(i, "\n");
}
But this will be O(n^2) (as pointed by #stefan) , you can also
addNewLinesToString(std::string& str, int sep)
{
string ans;
int i = 0;
while (i < str.size())
{
if (i % sep == 0 && i)
ans.push_back('\n');
ans.push_back(str[i]);
i++;
}
return ans;
}
Which uses more memory but is O(n).
Take a look at examples: http://www.cplusplus.com/reference/string/string/insert/

Answer 2

std::string insert_newlines(const std::string &in, const size_t every_n)
{
std::string out;
out.reserve(in.size() + in.size() / every_n);
for(std::string::size_type i = 0; i < in.size(); i++) {
if (!(i % every_n) && i) {
out.push_back('\n');
}
out.push_back(in[i]);
}
return out;
}
This:
allocates memory exactly once.
doesn't make the mistake of using int where size_t or std::string::size_type is required, so you don't run into strange problems for large strings or embedded platforms.
runs in linear O(n) time.
has an functional interface (rather than modifying the string in-place), an algorithm that modifies the input string and runs in O(n) time would be much more complex.

Answer 3

Try this function:
void addNewLinesToString(std::string* s, int change){
if(change <= 0)
return;
for(int i = 0; i < s.size(); i += change){
s.insert(i, "\n");
i++;
}
}
Edit: I don't know why your post got voted down, I up voted.

Answer 4

Maybe not fastest, but working:
void addNewLinesToString (std::string* txt, int limit)
{
if(limit <= 0)
return;
limit++;
for (int i=1; i<=txt->size()/limit; i++)
txt->insert((i*limit)-1, "\n");
}