C++ - Memory Allocation with a void pointer

[jdserran]

Good day, I need help ^__^
I have a void pointer: void *data;
I am told to "allocate len+1 characters and set the 'data' to the address of newly allocated memory setting the first character of 'data' to NULL (making the string blank)."

my guess is:

data = new char [len +1];
data[0] = 0;

Is my guess correct?

Thank you so much.

[JosAH]

Good day, I need help ^__^
I have a void pointer: void *data;
I am told to "allocate len+1 characters and set the 'data' to the address of newly allocated memory setting the first character of 'data' to NULL (making the string blank)."

my guess is:

data = new char [len +1];
data[0] = 0;

Is my guess correct?

Thank you so much.

No, sorry, it is not correct. Most likely you want to work/play with C type of strings.
A C 'string' basically is just a sequence of bytes and the last byte contains the
value 0 (or \0 for an alternative notation). So a string "foo" takes four chars, f, o,
o and \0.

Your 'data' pointer is a void pointer now; better make that a char pointer instead
so you refer to all the chars in the sequence it refers to:

char* data= malloc(len+1);
data[0]= 0; 
 

Those 'len+1' chars can contain a C string up to len+1 chars and the last byte
needs to be \0 char. Setting the first byte to \0 effectively 'constructs' an empty
C string.

You don't have to do that if you're sure that you're going to put a C string in that
area pointed by 'data'. The C string can contain 'len+1' chars including that trailing
\0 char.

For the memory allocation consistently choose either 'new' or 'malloc'. C just
uses 'malloc'; C++ prefers the 'new' operator.

kind regards,

Jos

[weaknessforcats]

C++ prefers the 'new' operator.

and that means not to use void* in the first place.

void pointers are used in C and not C++.

[jdserran]

umm, it's in the assignment specs so i think i don't have a choice, hehehe.

but thanks ^__^
The prof's going to post some code that he made just so we can be on the right track on doing the assignment, I'm just going to wait for that... He showed the starting codes (declaring the first 3 classes, setting up the constructors, etc.) but i forgot to copy the code for allocation with the void *data. I assumed that he's going to post them right away...

Thanks again JosAh and weaknessforcats ^__^

[weaknessforcats]

umm, it's in the assignment specs so i think i don't have a choice,

Tell your professor to remove void* from C++ problems. This is 2007 and not 1972 with an 8K computer. C++ has specific features (like function overloading) that removes the need foir a void*.