Question

I am reading an input file line by line by using ifstream and getline (say in string line). And I have to output string line to a file by removing first character of it. What I am doing is eraseing first character of line and outputting it using ofstream. Is there any better method to do it (means relatively faster one) ? I have millions of strings. (note that this is not true for all the lines, only for first line of every 10 line).

Answer 1

You could output the actual string pointer plus one:

outputStream << (line.c_str() + 1);

However, you should better check that the string is not empty first, or you might end up accessing an illegal pointer.

If you want to output a substring there’s the std::string::substr function. Or use the std::ostream::write function combined with the pointer arithmetic outlined above:

outputStream.write(line.c_str() + 1, 9);  /* 1st to 10th character */

For the above, you have to make sure the length of the string is at least ten characters.

Note: I personally would not use “hacks” as the ones outlined in this answer, unless in extreme situations. The substring function is there for a reason, and is the one I would recommend using.