typedef struct
{
char*title;
int year;
int length; //in minutes
} record;
record list[1024];
int j;
for(j=0;j<1024;++j)
list[j]=NULL;
I am trying to initialize an array of struct and let each element point to null initially. gcc gives me an error "incompatible types when assigning to type 'record' from type 'void*". How could I solve it? The purpose of doing this is when I access an element I am able to see if it has data or just empty.
You can initialize your array at declaration time this way:
record list[1024] = {{0}};
title member as a sentinel to mean an element has not been initialized: if (list[2].title == NULL)
list[2].title == 0 (or list[2].title == NULL), but the space is allocated.
record object with title==NULL, year==0, and length==0 could be a valid record.list[1024]; is array of object of your struct, which you access like
list[j].title;
list[j].year;
list[j].length;
What you are doing is:
list[j]=NULL
list[j] is of type record, NULL is void*. I guess this is not what you have in mind.
Either initialize individual elements in the struct by accessing them individually or use memset as suggested by others.
If you want to do it one at a time in a for loop, it would look like this
for(j=0;j<1024;++j)
list[j]=(record){0,0,0};
I would suggest using memset(list,0,1024*sizeof(record))
or bzero(list, 1024*sizeof(record))
If you want to do it with pointers, then you could declare your array like this:
record * list[1024];
Then you could set each one to NULL like you are and malloc each one when you're ready for it.
(record){0,0,0} is a C99 compound literal, not least because it probably isn't supported by MSVC. Is there a good reason to use 1024 * sizeof(record) rather than just sizeof(list), which will automatically change to the correct size if the dimension of list is changed from 1024 to some other number?
sizeof(list), it's just not what I familiar with. I would be most comfortable defining a macro for RECORDS_IN_LIST because I always feel bad if there is a number in my code that has no name. Then I would have RECORDS_IN_LIST*sizeof(record) which I find very readable.Your array is not an array of pointers to records, it is an array of record values. You cannot set the elements of the array to NULL because they are not pointers. This is not java...
memset(list, '\0', sizeof(list));.memset()records, it is an array ofrecordvalues. You cannot set the elements of the array toNULLbecause they are not pointers. This is not java...