C++之类和动态内存分配……
动态内存与类
stringbad.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
using namespace std;
class StringBad
{
private:
char *str;
int len;
static int num_strings;//不能对static变量在类定义中直接赋值，否则会报错，const除外
public:
StringBad(const char *s);
StringBad();
~StringBad();
friend ostream &operator<<(ostream &os, const StringBad &st);
};stringbad.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
int StringBad::num_strings = 0;
StringBad::StringBad(const char *s) // StringBad str("Hello world")
{
len = strlen(s);
str = new char[len + 1];
strcpy(str, s);
num_strings++;
cout << num_strings << ": \"" << str << ". \"" << endl;
}
StringBad::StringBad()
{
len = 4;
str = new char[4];
strcpy(str, "C++");
num_strings++;
cout << num_strings << ": \"" << str << ". \"" << endl;
}
StringBad::~StringBad()
{
cout << "\"" << str << "\" object deleted." << endl;
--num_strings;
cout << num_strings << " left." << endl;
delete []str;
}
ostream &operator<<(ostream &os, const StringBad &st)
{
os << st.str;
return os;
}vegnews.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
void callme1(StringBad &rsb);
void callme2(StringBad sb);
int main(void)
{
StringBad headline1("Hello world");
StringBad headline2("Good morning");
StringBad sports("I love you, Rick");
cout << "headline1: " << headline1 << endl;
cout << "headline2: " << headline2 << endl;
cout << "sports: " << sports << endl;
callme1(headline1);
callme2(headline2);
return 0;
}
void callme1(StringBad &rsb)
{
cout << "String passed by reference:" << rsb << endl;
}
void callme2(StringBad sb)
{
cout << "String passed by value: " << sb << endl;
}结果如下：
不能对static变量在类定义中直接赋值，否则会报错，static const类型除外。其通常在类的声明cpp文件中赋初始值一次
callme2(headline2)中使用直接赋值的方式相当于将StringBad sb=headline2，而这条语句会触发类的自动类型转换，即会调用符合条件的构造函数，但不存在符合条件的构造函数（符合条件的构造函数为StringBad(const StringBad &)）而当使用一个对象来初始化另一个对象时，编译器将自动生成上述构造函数，故实际只存在三个指针，但删除时却需要删除四个指针，故会发生报错
