【C++】-- STL之String详解（二）

1. size_t size() const;//size()求字符串中有效字符的个数
2. size_t length() const;//length()求字符串中有效字符的个数

1. #include<iostream>
2. #include<string>
3. using namespace std;
4. 
5. int main()
6. {
7.     string s1;
8.  cout << s1.size() << endl;
9.  cout << s1.length() << endl;
10.     
11.     return 0;
12. }

bool empty() const;//判断字符串是否为空

1.     string s1;
2.  cout << s1.empty() << endl;

size_t capacity() const;//返回所分配内存的字节数

1.     string s1("cplusplus.com");
2.     cout << s1.size() << endl;
3.  cout << s1.capacity() << endl;

void resize (size_t n);//将字符串大小调整为n个字符的长度，默认插入字符'\0',32位机器一般为4的倍数，64位机器一般为8的倍数，一般按2倍去调整

1.     string s1("cplusplus.com");
2.  s1.resize(20);
3.  cout << s1.size() << endl;
4.  cout << s1.capacity() << endl;

void resize (size_t n, char c);//将字符串大小调整为n个字符的长度，初始化新增空间的内容为c

1.     string s1("cplusplus.com");
2.  s1.resize(20, 'c');
3.  cout << s1 << endl;
4. 
5.  s1.resize(6);
6.  cout << s1 << endl;

void reserve (size_t n = 0);//调整容量，缺省容量为0

1.     string s1("cplusplus.com");
2. 
3.  s1.reserve(20);
4.  cout << "size:" << s1.size() << endl;
5.  cout << "capacity" << s1.capacity() << endl;
6. 
7.  s1.reserve(50);
8.  cout << "size:" << s1.size() << endl;
9.  cout << "capacity" << s1.capacity() << endl;

1. #include<iostream>
2. #include<string>
3. using namespace std;
4. 
5. int main()
6. {
7.  string s1;
8.  int oldCapacity = s1.capacity();
9.  for (char ch = 0; ch < 127; ch++)
10.   {
11.     s1 += ch;
12.     if (oldCapacity != s1.capacity())
13.     {
14.       cout << "增容：" << oldCapacity << "->" << s1.capacity() << endl;
15.       oldCapacity = s1.capacity();
16.     }
17.   }
18.   cout << s1 << endl;
19. 
20.   return 0;
21. }

1. #include<iostream>
2. #include<string>
3. using namespace std;
4. 
5. int main()
6. {
7.  string s1;
8.  s1.reserve(127);
9.  int oldCapacity = s1.capacity();
10. 
11.   for (char ch = 0; ch < 127; ch++)
12.   {
13.     s1 += ch;
14.     if (oldCapacity != s1.capacity())
15.     {
16.       cout << "增容：" << oldCapacity << "->" << s1.capacity() << endl;
17.       oldCapacity = s1.capacity();
18.     }
19.   }
20.   cout << s1 << endl;
21. 
22.   return 0;
23. }

1. #include<iostream>
2. #include<string>
3. using namespace std;
4. 
5. int main()
6. {
7.  string s1;
8.  s1.resize(127);
9.  int oldCapacity = s1.capacity();
10. 
11.   for (char ch = 0; ch < 127; ch++)
12.   {
13.     s1 += ch;
14.     if (oldCapacity != s1.capacity())
15.     {
16.       cout << "增容：" << oldCapacity << "->" << s1.capacity() << endl;
17.       oldCapacity = s1.capacity();
18.     }
19.   }
20.   cout << s1 << endl;
21. 
22.   return 0;
23. }