CODEWITHSUNDEEP
c++string
jmasterx
jmasterx

Reputation: 54123

Avoiding getting a substring?

I have a situation where I have a std::string, and I only need characters x to x + y, and I think it would speed it up quite a bit if I instead could somehow do (char*)&string[x], but the problem is all my functions expect a NULL terminated string.

What can I do?

Thanks

Upvotes: 0

Views: 123

Answers (5)

Jerry Coffin
Jerry Coffin

Reputation: 490178

You could overwrite &string[x+y+1] with a NUL, and pass &string[x] to your functions. If you're going to need the whole string again afterward, you can save it for the duration, and restore it when needed.

Upvotes: 0

Armen Tsirunyan
Armen Tsirunyan

Reputation: 133024

Nothing nice can be done. The only trick I can think of is temporarily setting s[x+y+1] to 0, pass &s[x], then restore the character. But you should resort to this ONLY if you are sure this will reasonably boost the performance and that boost is necessary

Upvotes: 3

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272517

You have no choice here. You can't create a null-terminated substring without copying or modifying the original string.

You say you "think it would speed it up". Have you measured?

Upvotes: 0

pm100
pm100

Reputation: 50190

nothing (if the string you need is in the middle). the speed difference will be utterly trivial unless its being done A LOT (several millions)

Upvotes: 1

Erik
Erik

Reputation: 91270

Use:

string.c_str() + x;

This assumes your function takes a const char *

If you need actual 0-termination, you'll have to copy.

Upvotes: 0

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