“error: assignment to expression with array type error” when I assign a struct field (C)

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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 <stdio.h>

#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?


Solution

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.[….]

Source: StackOverflow.com

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