面试：C++String类实现

 1 #include <iostream>
 2 #include <cstring>
 3 using namespace std;
 4 
 5 
 6 class CString {
 7 private:
 8     char* m_pdata;
 9 public:
10     CString(const char* ptr = nullptr) {
11         if (ptr == nullptr)  m_pdata = nullptr;
12         m_pdata = new char[strlen(ptr) + 1];
13         strcpy(m_pdata, ptr);
14     }
15     CString(const CString& a) {
16         if (a.m_pdata == nullptr) this->m_pdata = nullptr;
17         this->m_pdata = new char[strlen(a.m_pdata) + 1];
18         strcpy(this->m_pdata, a.m_pdata);
19     }
20 
21     CString(CString&& a){
22         this->m_pdata = a.m_pdata;
23         a.m_pdata = nullptr;
24     }
25 
26     ~CString() {
27         if (this->m_pdata){
28              delete[] this->m_pdata;
29         }
30     }
31 
32     CString& operator=(const CString& a) {
33         if (this == &a)
34             return *this;
35 
36         if (this->m_pdata)
37             delete[] this->m_pdata;
38         this->m_pdata = new char[strlen(a.m_pdata) + 1];
39         strcpy(this->m_pdata, a.m_pdata);
40         return *this;
41     }
42 
43     CString operator+=(const CString& a) {
44         if (a.m_pdata == nullptr) {
45             return *this;
46         } else if (this->m_pdata == nullptr) {
47             return a;
48         } else {
49             char* tmp = this->m_pdata;
50             this->m_pdata = new char[strlen(this->m_pdata) + strlen(a.m_pdata)
51                     + 1];
52             strcpy(this->m_pdata, tmp);
53             strcat(this->m_pdata, a.m_pdata);
54             delete[] tmp;
55             return *this;
56         }
57     }
58 
59     friend CString operator+(const CString& a, const CString& b) {
60         char* res = new char[strlen(a.m_pdata) + strlen(b.m_pdata) + 1];
61         strcpy(res, a.m_pdata);
62         strcat(res, b.m_pdata);
63         CString cs(res);
64         delete[] res;
65         return cs;
66     }
67 
68     friend ostream& operator<<(ostream& os, const CString& a) {
69         os << a.m_pdata;
70         return os;
71     }
72 };
73 
74 int main() {
75 
76     CString a("abc");
77     CString b(a);
78     a = b;
79     a += b;
80     CString c = a + b;
81     std::cout << c << std::endl;
82     std::cout << a << std::endl;
83 
84     return 0;
85 }