Question

void func(char* buf) { buf++;}

Should I call it passing by pointer or just passing by value(with the value being pointer type)? Would the original pointer passed in be altered in this case?

Answer 1

This is passing by value.

void func( char * b )
{
    b = new char[4];
}

int main()
{
    char* buf = 0;
    func( buf );
    delete buf;
    return 0;
}

buf will still be 0 after the call to func and the newed memory will leak.

When you pass a pointer by value you can alter what the pointer points to not the pointer itself.

The right way to do the above stuff would be

ALTERNATIVE 1

void func( char *& b )
{
    b = new char[4];
}

int main()
{
    char* buf = 0;
    func( buf );
    delete buf;
    return 0;
}

Notice the pointer is passed by reference and not value.

ALTERNATIVE 2

Another alternative is to pass a pointer to a pointer like

void func( char ** b )
{
    *b = new char[4];
}

int main()
{
    char* buf = 0;
    func( &buf );
    delete buf;
    return 0;
}

Please note I am not in any way advocating the use of naked pointers and manual memory management like above but merely illustrating passing pointer. The C++ way would be to use a std::string or std::vector<char> instead.