Writing to a const character pointer and does c_str provide the actual base address

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Hi,
My code snippet looks like this:

int main() {
        string s1("One\n");
	const char* s2 = s1.c_str();
	cout << s2 << s1;
	s2 = "Two\n";
	cout << s2 << s1;
}

Output:
One
One
Two
One

My doubts are:
-> Can we modify the const char* like shown above after initialization?!
-> Does the c_str() function return actual base address of string's character array?If yes then why is the s1 value not changed?

Thanks in advance

Posted 26-May-11 2:01am

hakz.code

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2 solutions

Solution 2

yes we can modify.

try the following code, but it is not safe.

MIDL

int _tmain(int argc, _TCHAR* argv[])
{
    std::string strName = "Sen SD";
    const char* pchName = strName.c_str();

    strcpy( const_cast<char*>( pchName ), "Ann" );

    return 0;
}

Posted 26-May-11 4:51am

SenAPI

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CPallini · Accepted Answer · 2011-05-26T02:14:00

HarishTheLearner wrote:
-> Can we modify the const char* like shown above after initialization?!

Yes, (like Obama) we can.

HarishTheLearner wrote:
does the c_str() function return actual base address of string's character array?If yes then why is the s1 value not changed?

Again, yes (see basic_string::c_str[^] documentation).

A little explanation:

C++

const char* s2 = s1.c_str();

Declares s2 as a pointer (a variable containing an address) to a (const) sequence of characters.
The same statement initializes it to point at s1 character sequence.

C++

s2 = "Two\n";

This change to s2 value modifies just the pointed address: now s2 points to the character sequence (the literal string) "Two\n", so that it points no more to s1 character sequence.

Now the output should be obvious.

BTW: never try to change the std::string content using the address provided by c_str() method.

:-)