一個C++類一般至少有四大函數(shù)，即構造函數(shù)、拷貝構造函數(shù)、析構函數(shù)和賦值函數(shù)，一般系統(tǒng)都會默認。但是往往系統(tǒng)默認的并不是我們所期望的，為此我們就有必要自己創(chuàng)造他們。在創(chuàng)造之前必須了解他們的作用和意義，做到有的放矢才能寫出有效的函數(shù)。

 #include <iostream>
 class CString
 {
   friend std::ostream & operator<<(std::ostream &, CString &);
   public:
     // 無參數(shù)的構造函數(shù)
     CString();
     // 帶參數(shù)的構造函數(shù)
     CString(char *pStr);
     // 拷貝構造函數(shù)
     CString(const CString &sStr);
     // 析構函數(shù)
     ~CString();
     // 賦值運算符重載
     CString & operator=(const CString & sStr);
   private:
     char *m_pContent;
 };
 inline CString::CString()
 {
   printf("NULL\n");
   m_pContent = NULL;
  m_pContent = new char[1];
  m_pContent[0] = '\0';
 }
 inline CString::CString(char *pStr)
 {
   printf("use value Contru\n");
   m_pContent = new char[strlen(pStr) + 1];
   strcpy(m_pContent, pStr);
 }
 inline CString::CString(const CString &sStr)
 {
   printf("use copy Contru\n");
   if(sStr.m_pContent == NULL)
     m_pContent == NULL;
   else
   {
     m_pContent = new char[strlen(sStr.m_pContent) + 1];
     strcpy(m_pContent, sStr.m_pContent);
   }
 }
 inline CString::~CString()
 {
   printf("use ~ \n");
   if(m_pContent != NULL)
     delete [] m_pContent;
 }
 inline CString & CString::operator = (const CString &sStr)
 {
   printf("use operator = \n");
   if(this == &sStr)
     return *this;
   // 順序很重要，為了防止內(nèi)存申請失敗后，m_pContent為NULL
  char *pTempStr = new char[strlen(sStr.m_pContent) + 1];
   delete [] m_pContent;
   m_pContent = NULL;
   m_pContent = pTempStr;
   strcpy(m_pContent, sStr.m_pContent);
   return *this;
 }
 std::ostream & operator<<(std::ostream &os, CString & str)
 {
   os<<str.m_pContent;
   return os;
 }
 int main()
 {
  CString str3; // 調(diào)用無參數(shù)的構造函數(shù)
   CString str = "My CString!"; // 聲明字符串，相當于調(diào)用構造函數(shù)
  std::cout<<str<<std::endl;
   CString str2 = str; // 聲明字符串，相當于調(diào)用構造函數(shù)
   std::cout<<str2<<std::endl;
   str2 = str;  // 調(diào)用重載的賦值運算符
  std::cout<<str2<<std::endl;
   return 0;
 }

輸出：

NULL
use value Contru
My CString!
use copy Contru
My CString!
use operator =
My CString!
use ~
use ~
use ~

以上所述是小編給大家介紹的從string類的實現(xiàn)看C++類的四大函數(shù)(面試常見)的全部敘述，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！

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