In c I am trying to assign a char array inside a struct with a user provided value, here is my code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct person 
{
       char name[20];
       int age;
};

struct person *assign(char arr[], int age) 
{
       struct person *x = malloc(sizeof(struct person));

       x->name[20] = arr[20];
       x->age = 21;

       return x;
}


int main()
{

     char name[20] = "Arthur morgan";
     int age = 34;

     struct person* person1 = assign(name, age);

     printf("name: %s\n", person1->name);
     printf("age: %d\n", person1->age);


     return 0;
}

The problem is that the name prints nothing for some reason, the age however prints as expected.

Why is the name not printing correctly?

CodePudding user response：

x->name[20] = arr[20];

1. It does not copy the array
2. It copies 1 character and you are accessing array outside its bounds which is undefined behaviour (UB)
3. It is better to use objects not types in sizeof
4. Always check the result of malloc

You need to copy the string using strcpy function

struct person *assign(char arr[], int age) 
{
    struct person *x = malloc(sizeof(*x));
    if(x)
    {
        strcpy(x->name,arr);
        x->age = 21;
    }

    return x;
}

https://godbolt.org/z/vKddb4b9a