I got a chars array like
char ch[] = "This is a char array";
and I want to make a new string from index n to index j, for i.e.
string str = stringFromChar(ch, 0, 5); //str = 'This'
4 Answers
You could use the constructor for std::string that takes two iterators.
std::string str(std::begin(ch), std::next(std::begin(ch), 5));
In the more general case, you could use std::next for both the start and end iterator to make a string from an arbitrary slice of the array.
I prefer to use the C++ Standard Library when applicable, but know that you could do the same thing with pointer arithmetic.
std::string str(ch, ch+5);
3 Comments
Humam Helfawi
BTW, what is diffrent between std::next(std::begin(ch), 5) and std::begin(ch)+ 5 ?
Cory Kramer
@HumamHelfawi
std::next and std::advance handle advancing through a container that may or may not use contiguous memory (i.e. a std::list, etc).Humam Helfawi
Oh my god I was always using the + way and I thought that my code run for any container.. Foolish me! Thanks!
You can just write
string str(ch, ch + 5); //str = 'This'
That is the general form will look like
string str(ch + i, ch + j); //str = 'This'
where i < j
If the first index is equal to 0 then you can also write
string str(ch, n );
where n is the number of characters that you are going t0 place in the created object. For example
string str( ch, 4 ); //str = 'This'
Or if the first index is not equal to 0 then you can also write
string str( ch + i, j - i ); //str = 'This'
answered Oct 25, 2015 at 15:43
Vlad from Moscow
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Comments
Just use the constructor with iterators ( also, char* is a valid input iterator )
std::string str(ch, ch + 5);
Comments
You can just use the begin and end functions...
#include<iostream>
#include<string>
int main() {
char ch[] = "This is a char array";
std::string str(std::begin(ch), std::end(ch));
std::cout << str << std::endl;
// system("pause");
return 0;
}
char[] chthis is not a valid syntax. maybe in C#, but not in C++