Char array in a struct - incompatible assignment

Question

I tried to find out what a struct really  is  and hit a problem  so I have really 2 questions   1  What is saved in  sara   Is it a pointer to the first element of the struct   2  The more interesting question  Why doesn t it compile   GCC says  test c 10  error  incompatible types in assignment  and I can t figure out why     This part has been solved by your answers already  great     include  lt stdio h gt   struct name       char first 20       char last 20       int main         struct name sara      sara first    Sara       sara last    Black       printf  struct direct   x n  sara        printf  struct deref   x t s n    sara   sara         Thanks for your help

User · Accepted Answer

This has nothing to do with structs - arrays in C are not assignable   char a 20   a    foo        error   you need to use strcpy   strcpy  a   foo       or in your code   strcpy  sara first   Sara

User · Answer

You can use strcpy to populate it  You can also initialize it from another struct    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   struct name       char first 20       char last 20       int main         struct name sara      struct name other       strcpy sara first  Sara        strcpy sara last   Black         other   sara       printf  struct   s t s n   sara first  sara last       printf  other struct   s t s n   other first  other last

User · Answer

You can try in this way  I had applied this in my case     include lt stdio h gt   struct name      char first 20      char last 30          globally     struct name sara   Sara   Black     int main          locally  struct name sara   Sara   Black      printf   s  sara first    printf   s  sara last

User · Answer

The Sara structure is a memory block containing the variables inside  There is nearly  no difference between a classic declarations    char first 20   int age    and a structure    struct Person  char first 20   int age       In both case  you are just allocating some memory to store variables  and in both case there will be 20 4 bytes reserved  In your case  Sara is just a memory block of 2x20 bytes    The only difference is that with a structure  the memory is allocated as a single block  so if you take the starting address of Sara and jump 20 bytes  you ll find the  last  variable  This can be useful sometimes   check http   publications gbdirect co uk c book chapter6 structures html for more

User · Answer

Or you could just use dynamic allocation  e g    struct name     char  first    char  last      struct name sara  sara first    Sara   sara last    Black   printf  first   s  last   s n   sara first  sara last

User · Answer

sara is the struct itself  not a pointer  i e  the variable representing location on the stack where actual struct data is stored   Therefore   sara is meaningless and won t compile

User · Answer

use strncpy to make sure you have no buffer overflow   char name     whatever you want   strncpy  sara first  name  sizeof sara first -1    sara first sizeof sara first -1    0

User · Answer

You can also initialise it like this   struct name sara      Sara    Black       Since  as a special case  you re allowed to initialise char arrays from string constants   Now  as for what a struct actually is - it s a compound type composed of other values   What sara actually looks like in memory is a block of 20 consecutive char values  which can be referred to using sara first  followed by 0 or more padding bytes  followed by another block of 20 consecutive char values  which can be referred to using sara last    All other instances of the struct name type are laid out in the same way   In this case  it is very unlikely that there is any padding  so a struct name is just a block of 40 characters  for which you have a name for the first 20 and the last 20   You can find out how big a block of memory a struct name takes using sizeof struct name   and you can find out where within that block of memory each  member of the structure is placed at using offsetof struct name  first  and offsetof struct name  last

[c] Char array in a struct - incompatible assignment?

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