atoi in std:string

How do I perform atoi on std:string

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

Code:

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

using namespace std;

int main()
{
        string s("23");

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

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is there a soloution without casting?

Quote:

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Originally posted by avi123
is there a soloution without casting?

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What casting?

Regards,

Paul McKenzie

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

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

so it's not expensive, right?

Quote:

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

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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

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)

Quote:

---

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)

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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

so is it safe to use c_csr and then atoi?

Quote:

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

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Yes...