CODEWITHSUNDEEP
cpointersc-strings
user5562628
user5562628

Reputation:

Returning pointers in C

So I am new to C and I have a question that I am hoping someone can help me with. Suppose I have a string. 

typedef struct String {
    char *value;
    int size;
} String;

And what I want to do is initialize this string with a function. My first question is which would be better 

bool init_String(String **s, char *p) {
    if (s == NULL || *s == NULL) {
        return false;
    }
    (*s)->value = p;
    (*s)->size = strlen(p);
    return true;
}

In this version the function takes a pointer to a pointer and doesn't return the string. My other version is this one:

String *init_String(String **s, char *p) {
    if (s == NULL) {
        return NULL;
    }
    s->value = p;
    s->size = strlen(p);
    return s;
}

Which is better for the user? My second question is is it better to malloc according to the user or according to me. In other words should the user malloc a String and then pass it to the init function or should the init function work as alloc_init and do both the call to malloc and the string initialization?

Thanks

Upvotes: 1

Views: 95

Answers (1)

John Zwinck
John Zwinck

Reputation: 249642

How about this?

typedef struct String {
  char *value;
  size_t size;
  int ref; // if nonzero, do not free(value)
} String;

String refer_String(const char *p) {
  String out = { p, strlen(p), 1 };
  return out;
}

String copy_String(const char *p) {
  String out = { strdup(p), strlen(p), 0 };
  return out;
}

void free_String(const String *s) {
  if (!s->ref) {
    free(s->value);
  }
}

This provides a way to refer to existing literal strings like your original code, but also a way to create new strings which may be modified.

Upvotes: 3

Related Questions