incrementing char pointers

[rushilsharma]

hello,
I was playing around with char pointers. I wanted to increment each letter of a char array by 1 character. i.e. 'hello' becomes 'ifmmp' (i = h+1)and here is a small code i wrote :


char *rushil = "hello";

while(*rushil != '\0')
{
++(*rushil); // run time error in this line dev C++ crashes
rushil++;
}

i am not sure but the program hangs on the line ++(*rushil).
I also tried :

*rushil = *rushil +sizeof(char); but error again

please help in terms of logic.
Thank you

[wolfgang]

You are trying to change a constant char string. You need to define the string in writable memory in order to edit it.

#include <iostream>
#include <cstring>

int main()
{
	char buffer[16] = "hello";
	char *cstr = new char[16];
	memcpy(cstr, buffer, 16);
	char *p = cstr;

	while (*p != '\0')
	{
		++(*p);
		++p;
	}

	std::cout << cstr << std::endl;
	delete[] cstr;
}

[rushilsharma]

oh.. ok.

but doesn't the char pointer (in my code) point to a fixed address and the value stored in the address can change?
Thanks,
-Rushil

[Athar]

and the value stored in the address can change?

You can't change it, because string literals are constant as wolfgang already said (that means they can be in memory sections that are read-only).

Conversion to a pointer to non-const char is only allowed for compatibility reasons and your compiler should warn you about it ("warning: deprecated conversion from string constant to ‘char*’"). Trying to modify the string results in undefined behavior.

[Galik]

In your code the string is likely to be stored in 'read only' memory that will throw a memory protection fault if you attempt to change it.

Also you might consider using std::string instead:

#include <string>
#include <iostream>

int main()
{
	std::string rushil = "hello";

	for(size_t i = 0; i < rushil.length(); ++i)
	{
	    ++rushil[i];
	}

	std::cout << rushil << '\n';
}

[rushilsharma]

ohh... ok.. thank you all for ur help.. i think i understand..