以下是引用ljhwahaha在2007-4-8 13:20:26的发言：
这是书本上的代码`` 我想问的是红字部分，为什么要用常应用呢，似乎直接用值传递也可以达到同样的效果；
还有书上的运行结果是
size:0
length:0
capacity:0
max size:4294967293
size:16
length:16
capacity:31
max size:4294967293
size:10
length:10
capacity:31
max size:4294967293 //在VC++6.0下调试和这个相同
但我运行后的结果是
size:0
length:0
capacity:15
max size:4294967294
size:16
length:16
capacity:31
max size:4294967294
size:10
length:10
capacity:15
max size:4294967294
（我用的是vc++2005）为什么会不一样呢？//在VC++2005下调试会出现错误.
#include <iostream>
#include <string>
using namespace std;
void PrintAttribute(const string &str); //consgt ?
void main()
{
string s1,s2;
PrintAttribute(s1);
s1="My string object";
PrintAttribute(s1);
s2="new string";
PrintAttribute(s2);
system("pause");
}
void PrintAttribute(const string &str)
{
cout<<"size:"<<str.size()<<endl;
cout<<"length:"<<str.length()<<endl;
cout<<"capacity:"<<str.capacity()<<endl;
cout<<"max size:"<<str.max_size()<<endl;
}
下面是MSDN中查到的有关capacity 资料
Standard C++ Library Reference
basic_string::capacity
Returns the largest number of elements that could be stored in a string without increasing the memory allocation of the string.
size_type capacity( ) const;
Return Value
The size of storage currently allocated in memory to hold the string.
Remarks
The member function returns the storage currently allocated to hold the controlled sequence, a value at least as large as size.
Example
Copy Code
// basic_string_capacity.cpp
// compile with: /EHsc
#include <string>
#include <iostream>
int main( )
{
using namespace std;
string str1 ("Hello world");
cout << "The original string str1 is: " << str1 << endl;
// The size and length member functions differ in name only
basic_string <char>::size_type sizeStr1, lenStr1;
sizeStr1 = str1.size ( );
lenStr1 = str1.length ( );
basic_string <char>::size_type capStr1, max_sizeStr1;
capStr1 = str1.capacity ( );
max_sizeStr1 = str1.max_size ( );
// Compare size, length, capacity & max_size of a string
cout << "The current size of original string str1 is: "
<< sizeStr1 << "." << endl;
cout << "The current length of original string str1 is: "
<< lenStr1 << "." << endl;
cout << "The capacity of original string str1 is: "
<< capStr1 << "." << endl;
cout << "The max_size of original string str1 is: "
<< max_sizeStr1 << "." << endl << endl;
str1.erase ( 6, 5 );
cout << "The modified string str1 is: " << str1 << endl;
sizeStr1 = str1.size ( );
lenStr1 = str1.length ( );
capStr1 = str1.capacity ( );
max_sizeStr1 = str1.max_size ( );
// Compare size, length, capacity & max_size of a string
// after erasing part of the original string
cout << "The current size of modified string str1 is: "
<< sizeStr1 << "." << endl;
cout << "The current length of modified string str1 is: "
<< lenStr1 << "." << endl;
cout << "The capacity of modified string str1 is: "
<< capStr1 << "." << endl;
cout << "The max_size of modified string str1 is: "
<< max_sizeStr1 << "." << endl;
}
Sample Output
The original string str1 is: Hello world
The current size of original string str1 is: 11.
The current length of original string str1 is: 11.
The capacity of original string str1 is: 15.
The max_size of original string str1 is: 4294967294.
The modified string str1 is: Hello
The current size of modified string str1 is: 6.
The current length of modified string str1 is: 6.
The capacity of modified string str1 is: 15.
The max_size of modified string str1 is: 4294967294.
[此贴子已经被作者于2007-4-8 14:29:51编辑过]
