CODEWITHSUNDEEP
c++
user1838343
user1838343

Reputation: 449

c++: writing strings to file by removing first char

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).

Upvotes: 0

Views: 1104

Answers (4)

jrok
jrok

Reputation: 55415

I'd try the simplest approach first and see if it's fast enough:

if (!mystring.empty())
    std::copy( mystring.begin() + 1, mystring.end(),
        std::ostreambuf_iterator<char>(stream_object) );

You'll need <algorithm> and <iterator> headers.

Upvotes: 2

Some programmer dude
Some programmer dude

Reputation: 409356

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.

Upvotes: 1

borisbn
borisbn

Reputation: 5054

Maybe the fastest way to write whole string without 1st char is from @JoachimPileborg answer. But if you want to write 10 chars from 1st to 10th, then the fastest way is to use fwrite function instead of fstream.

fwrite( line.c_str() + 1, 1, 10, file );

Pay an attention, that you should use it very accurate. You should be assured, that line has more then 10 chars.

Upvotes: 0

&#193;kos
&#193;kos

Reputation: 3221

I assume you are using std::string...

std::string str;  // contains the line
str.substr (1, str.length() - 1); // gives you what you need

Best, Akos

Upvotes: 0

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