Question

What is the standard way to copy two structs that contain char arrays?

Here is some code:

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

typedef struct {
    char* name;
    char* surname;
} person;

int main(void){
    person p1;
    person p2;

    p1.name     = (char*)malloc(5);
    p1.surname  = (char*)malloc(5);

    strcpy(p1.name, "AAAA");
    strcpy(p1.surname, "BBBB");

    memcpy(&p2, &p1, sizeof(person));
    free(p1.name);
    printf("%s\n", p2.name);
    return 0;
}

The line printf("%s\n", p2.name); does not print something, because I freed the buffer.

The problem with my structs is that they are bigger than struct person. They contain hundreds of char pointers, and I have to copy every member one by one.

Is there another way to copy two structs that contain char arrays without using malloc and strcpy for every member?

Answer 1

You have no choice but provide a copy function yourself:

void copy_person(person *dst, const person *src)
{
    dst->name = malloc(strlen(src->name) + 1);
    dst->surname = malloc(strlen(src->surname) + 1);
    strcpy(dst->name, src->name);
    strcpy(dst->surname, src->surname);
}

which may be more elaborated than that: checking for errors, factoring the strlen + strcpy in an auxilliary function, etc.

That’s what copy constructors in C++ are for.