C struct problem

Question

I am trying to learn about structs in C, but i do not understand why i cannot assign the title as i my example:

#include <stdio.h>

struct book_information {
 char title[100];
 int year;
 int page_count;
}my_library;


main()
{

 my_library.title = "Book Title"; // Problem is here, but why?
 my_library.year = 2005;
 my_library.page_count = 944;

 printf("\nTitle: %s\nYear: %d\nPage count: %d\n", my_library.title, my_library.year, my_library.page_count);
 return 0;
}

Error message:

books.c: In function ‘main’:
books.c:13: error: incompatible types when assigning to type ‘char[100]’ from type ‘char *’

Answer 1

LHS is an array, RHS is a pointer. You need to use strcpy to put the pointed-to bytes into the array.

strcpy(my_library.title, "Book Title");

Take care that you do not copy source data > 99 bytes long here as you need space for a string-terminating null ('\0') character.

The compiler was trying to tell you what was wrong in some detail:

error: incompatible types when assigning to type ‘char[100]’ from type ‘char *’

Look at your original code again and see if this makes more sense now.

Answer 2

As the message says, the issue is you are trying to assign incompatible types: char* and char[100]. You need to use a function like strncpy to copy the data between the 2

strncpy(my_library.title, "Book Title", sizeof(my_library.title));