remove char from stringstream and append some data

Question

In my code there is a loop that adds sth like that "number," to stringstream. When it ends, I need to extract ',' add '}' and add '{' if the loop is to repeated.

I thought i can use ignore() to remove ',' but it didn't work. Do you know how I can do what I describe?

example:

douCoh << '{'; for(unsigned int i=0;i<dataSize;i++)   if(v[i].test) douCoh << i+1 << ','; douCoh.get(); douCoh << '}'; 

Answer 1

You can seek the stringstream and go back 1 character, using stringstream::seekp. Note that it does not remove the last character, but only moves the write head. This is sufficient in this case, as we overwrite the last character with an }.

douCoh << '{'; for(unsigned int i=0;i<dataSize;i++)   if(v[i].test) douCoh << i+1 << ','; douCoh.seekp(-1,douCoh.cur); douCoh << '}'; 

Answer 2

You can extract the string (with the str() member), remove the last char with std::string::erase and then reset the new string as buffer to the std::ostringstream.

However, a better solution would be to not insert the superfluous ',' in the first place, by doing something like that :

std::ostringstream douCoh; const char* separator = "";  douCoh << '{'; for (size_t i = 0; i < dataSize; ++ i) {   if (v[i].test)   {     douCoh << separator << i + 1;     separator = ",";   } } douCoh << '}';