char initialization constructor in c++

Question

I have write this constructor to initialize the character type array

class StudentInfo
{
  char* vuId;
public:
  StudentInfo(char* vu_Id)
  {
    setVuId(vu_Id);
  }
  void setVuId(char* vu_Id)
  {
    vuId = new char[strlen(vu_Id) + 1];
    strcpy(vuId, vu_Id);
  }
};

This code is working fine. but I want to initialize without having to call setVuId function. Is there anyway to do it?

Move `setVuId`'s body into constructor? Also suggest use `std::string` instead. — awesoon, Jun 24 '13 at 12:56
Can I question your desire to avoid calling setVuId in the first place? — Sebastian Redl, Jun 24 '13 at 13:30

Balog Pal · Answer 1 · 2013-06-24T14:38:47.080

8

sure:

#include <string>

class StudentInfo
{
  std::string vuId;
public:
  explicit StudentInfo(const char* vu_Id) : vuId(vu_Id) {}

};

edited Jun 24 '13 at 14:38

answered Jun 24 '13 at 12:56

Balog Pal

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Can you explain the meaning of last line ? I know its a constructor with a pointer to const charcter parameter but what is " : vuId(vu_Id)" – Vivek Sadh Jun 24 '13 at 13:16
@Vivek: it passes the argument to the constructor of std::string when member vuID is constructed. google for 'c++ contsructor initialization list' for more details – Balog Pal Jun 24 '13 at 13:20
Hey Pal - make the constructor explicit, maybe? – doctorlove Jun 24 '13 at 14:37
@doctorlove: good point :) – Balog Pal Jun 24 '13 at 14:39

bobah · Answer 2 · 2013-06-24T15:10:49.000

0

Use std::string if you can tolerate copy-on-write and associated overhead, else use this:

#include <cstring>

class StudentInfo
{
  size_t len;
  char* data;

public:
  StudentInfo(char* vu_Id):
    len(vu_Id ? strlen(vu_Id) : 0),
    data(len ? (char*)memcpy(new char[len + 1], vu_Id, len + 1) : 0)
  {
  }

  virtual ~StudentInfo() {
    delete [] data;
  }
}

edited Jun 24 '13 at 15:10

answered Jun 24 '13 at 13:05

bobah

17,620
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5

IIRC C++11 does not allow COW for ``std::string``. – juanchopanza Jun 24 '13 at 13:09
yes, on the paper, http://stackoverflow.com/questions/12520192/is-stdstring-refcounted-in-gcc-c11 – bobah Jun 24 '13 at 13:26
1

replace strncpy with memcpy and take care of Rule of 3 – Balog Pal Jun 24 '13 at 13:43
1

gcc does COW, MSVC the small string optimisation – doctorlove Jun 24 '13 at 14:37

char initialization constructor in c++

2 Answers2