error assignment to expression with array type error when I assign a struct field C

Question

I m a beginner C programmer  yesterday I learned the use of C structs and the possible application of these ones about the resolution of specific problems  However when I was experimenting with my C IDE  Codeblocks 16 01  in order to learn this aspect of C programming  I ve encountered a strange issue  The code is the following    include  lt stdio h gt    define N 30  typedef struct       char name N        char surname N        int age    data   int main          data s1       s1 name  Paolo        s1 surname    Rossi        s1 age   19       getchar         return 0      During the compilation  the compiler  GCC 4 9 3-1 under Windows  reported me an error that says       error  assignment to expression with array type error     on instruction   s1 name  Paolo   s1 surname  Rossi     while if I do  data s1     Paolo    Rossi   19     it works   What am I doing wrong

User · Accepted Answer

You are facing issue in   s1 name  Paolo     because  in the LHS  you re using an array type  which is not assignable   To elaborate  from C11  chapter   6 5 16     assignment operator shall have a modifiable lvalue as its left operand    and  regarding the modifiable lvalue  from chapter   6 3 2 1     A modifiable lvalue is an lvalue that   does not have array type          You need to use strcpy   to copy into the array   That said  data s1     Paolo    Rossi   19   works fine  because this is not a direct assignment involving assignment operator  There we re using a brace-enclosed initializer list to provide the initial values of the object  That follows the law of initialization  as mentioned in chapter   6 7 9     Each brace-enclosed initializer list has an associated current object  When no   designations are present  subobjects of the current object are initialized in order according   to the type of the current object  array elements in increasing subscript order  structure   members in declaration order  and the first named member of a union

User · Answer

Please check this example here  Accessing Structure Members  There is explained that the right way to do it is like this    strcpy s1 name    Egzona    printf   Name    s n   s1 name

User · Answer

typedef struct       char name 30        char surname 30        int age    data    defines that data should be a block of memory that fits 60 chars plus 4 for the int  see note    ---------------------------- ------------------------------ ----     this is name                this is surname                this is age   This allocates the memory on the stack   data s1    Assignments just copies numbers  sometimes pointers   This fails   s1 name    Paulo     because the compiler knows that s1 name is the start of a struct 64 bytes long  and  Paulo  is a char   6 bytes long  6 because of the trailing  0 in C strings  Thus  trying to assign a pointer to a string into a string   To copy  Paulo  into the struct at the point name and  Rossi  into the struct at point surname   memcpy s1 name      Paulo   6   memcpy s1 surname   Rossi   6   s1 age   1    You end up with   Paulo0---------------------- Rossi0------------------------- 0001    strcpy does the same thing but it knows about  0 termination so does not need the length hardcoded   Alternatively you can define a struct which points to char arrays of any length   typedef struct     char  name    char  surname    int age    data    This will create   ---- ---- ----    This will now work because you are filling the struct with pointers   s1 name    Paulo   s1 surname    Rossi   s1 age   1    Something like this   ---4 --10 ---1    Where 4 and 10 are pointers   Note  the ints and pointers can be different sizes  the sizes 4 above are 32bit as an example

[c] "error: assignment to expression with array type error" when I assign a struct field (C)

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