atoi in std:string

[avi123]

How do I perform atoi on std:string

[sbrothy]

Did you try std::string::c_str() method:

#include <cstdlib>
#include <string>
#include <iostream>

using namespace std;

int main() 
{
	string s("23");

	cout << atoi(s.c_str()) << endl;
	
	return 0;
}

[avi123]

is there a soloution without casting?

[Paul McKenzie]

Originally posted by avi123
is there a soloution without casting?

What casting?

Regards,

Paul McKenzie

[avi123]

I mean without using c_str
is this an 'expensive' function?

[AvDav]

In MS-STL it conditionaly returns pointer, in SGI -- just returns it.

[avi123]

so it's not expensive, right?

[Paul McKenzie]

Originally posted by avi123
so it's not expensive, right?

How many times are you expecting to use c_str()? I would argue that atoi() is an "expensive" function, and c_str() adds no overhead, but that depends on the implementaion of std::string.

In any event, to get a const char * from a std::string, you must call c_str(), and this is what atoi() is expecting.

Regards,

Paul McKenzie

[avi123]

Paul

I must use atoi or eqvivalent function
I have std:string and not char *, if there is no way to do it directly on the std:string then I'll use c_cstr and then atoi,
but I must perform atoi (or similar function)

[Paul McKenzie]

Originally posted by avi123
Paul

I must use atoi or eqvivalent function
I have std:string and not char *, if there is no way to do it directly on the std:string then I'll use c_cstr and then atoi,
but I must perform atoi (or similar function)

Your only choice is to use c_str(). The buffer for a std::string is not guaranteed to be contiguous, so getting a direct pointer to the buffer is not guaranteed to work. Also, the buffer for a std::string is more than likely a private member variable, therefore you don't have access to it.

An implementation of a string class (even though it isn't called std::string) called the std::rope (http://www.sgi.com/tech/stl/Rope.html)
that SGI STL supports, is an example where the characters for the string are not stored in a contiguous buffer.

Regards,

Paul McKenzie

[avi123]

so is it safe to use c_csr and then atoi?

[Andreas Masur]

Originally posted by avi123
so is it safe to use c_csr and then atoi?

Yes...