Alternative strdup

Question

I am writing a C ++ class for a book containing the name:

class Book {
private:
    char* nm;
..........
............
..........
...........
};

I am not allowed to use std::stringin this appointment. Therefore, here I use strdupto copy the value of the parameter name in nm in the constructor:

Book::Book(const char *name, int thickness, int weight)
    : nm(NULL)
    , thck(thickness)
    , wght(weight)
{
    if (name)
        nm = strdup(name);
}

Is there an alternative to achieve the same result without using strdup, but use a keyword instead new?

Answer 1

Strictly speaking: a class stringis part of a string library. This is much easier to use, dynamic in nature, and you have less worry about copying / assigning than in C-style strings.

:

class Book {
   public:
     Book(const char *name, ...) : nm(0), ... {
           if (!name) throw "invalid parameter";
           nm = new char [ strlen(name) + 1 ];
           strcpy(nm, name);
     }
     ~Book() {
           delete [] nm;
           // ...
     }
     Book(Book const& o) : nm(0), ... {
           if (!name) throw "invalid parameter";
           char *p = new char [ strlen(name) + 1 ];
           if (p) {
               strcpy(p, name);
               delete [] nm;
               nm = p; 
           }
     }
     Book& operator=(Book const& o) {
           if (this != &o) {
              char *p = new char [ strlen(name) + 1 ];
              if (p) {
               strcpy(p, name);
               delete [] nm;
               nm = p; 
              }
           }
           return *this;             
     }
 };

, Big-three ( , ).

Answer 2

, dirkgently, : , .

- , , , , . , C , , :

class Book {
    char *nm;
public:
    Book(const char *name) : nm(copystr(name)) { /* don't throw an exception! */ }
    Book(const Book &o) : nm(copystr(o.nm)) { /* Likewise! */ }
    ~Book() { delete[] nm; }
    Book& operator=(const Book &o) {
       // this is called copy-and-swap (CAS). If you absolutely
       // have to write this kind of resource-managing code, then
       // you will need this technique, because it the best
       // way to provide the strong exception guarantee.
       Book cp = o;
       swap(cp);
       return *this;
    }
    /* or you can do this:
    Book& operator=(Book cp) {
       swap(cp);
       return *this;
    }
    */
    void swap(Book &o) {
       std::swap(this->nm, o.nm);
       // also swap other members
    }
};

char *copystr(const char *name) {
    if (!name) return 0;
    char *newname = new char[strlen(name)+1];
    std::strcpy(newname, name);
    return newname;
}

. " !" ? , , . , , , . - , , Book. , , . , TR1.

, , , , =, :

class Book {
    char *nm;
public:
    Book(const char *name) : nm(copystr(name)) { }
    ~Book() { delete[] nm; }
private:
    Book(const Book &o);
    Book& operator=(const Book &o);
};

, strdup . ( GNU), "strdup.c". , , , : "function_name.c", , , GNU, , , , . malloc .

http://www.koders.com/c/fidF16762E3999BA95A0B5D87AECB0525BA67CEE45A.aspx

http://cvs.frodo.looijaard.name/viewvc/cgi-bin/viewvc.cgi/public/psiconv/compat/strdup.c?revision=1.1.1.1&view=markup

Answer 3

, .

• ,
• copy the contents of the string to this array
• point nmto the selected array

Or you can use strdup- btw is strdupnot included C++ STL.

Answer 4

You should malloc with strlen and then use strcopy. Stupid homework by the way.

Answer 5

Book::Book(const char *name, int thickness, int weight):nm(NULL), thck(thickness), wght(weight){ 
  if (name) {
     size_t length = strlen(name);
     nm = new char[length + 1];
     memcpy(nm, name, length + 1);
  }