Thread: Assign array to another.

Hi, i am trying to get one char array to be assigned to another.
I have a struct called root which has a field called num, this is a char array of length 12.
One function i have tries to double the length of the char array by creating a new one double the size and copies everything in the first array into the new one, as well as some more chars. At the end i try:

Code:

root->num = newNum ;

but this won't compile, i get incompatible types in assignment!
any help would be great, i'm quite new to C so be nice :P
-ed

You can't assign to arrays like that, you can copy one to another using strcpy() otherwise you'll get the "incompatible types" compile time error.
OTOH you can assign to structs. If both arrays, num and newNum, are the only members of struct root then you can assign one struct to another.
The net effect of the struct assignment will be that array newNum will get copied into array num.

Originally Posted by boblettoj99

the struct has more fields, which cancels out that idea i assume. How would i go about using strcpy()? And will this make the num field have 24 characters instead of 12 or will it just loop round and start at the beginning of the array after 12 characters?

Neither, what will end up happening is a segfault because you have stepped out of bounds of array num[]. You can't stuff more than what you have allocated for num[].

Originally Posted by boblettoj99

EDIT:

tried:

Code:

strcpy(root->num , newNum)

but the array is still only 12 chars, but its content hasn't changed either...weird!

Aren't the first 12 elements of num[] and newNum[] identical?

Yeh, sorry, it's doing what it should. Is there any way i can make this work then? Other than making num have a ridiculous amount of space in the struct definition?

EDIT: (assuming i run this function an unknown number of times)

Short answer, you can't.

to do what you want, you can

memcpy((void*)root->num, (void*)newNum, sizeof(newNum));

which implies that newNum is an array and not a pointer. If newNum is a pointer you need a size_t len of newNum.

argh, ok, well i'll have to find some new way of getting round this problem then, thanks for the help!

Originally Posted by boblettoj99

Yeh, sorry, it's doing what it should. Is there any way i can make this work then? Other than making num have a ridiculous amount of space in the struct definition?

EDIT: (assuming i run this function an unknown number of times)

Not sure what you mean by the above statement