std::string你也许不知道的秘密

OwnWaterloo

c_str() 返回一个数组， 保证有size()+1个元素， 前size()个元素是字符串内容（可能有0）， s.c_str()[size()] 是0 。
而data() 返回一个数组。 如果size()>0 则保证有size()个元素， 前size个元素是字符串内容， 没说它不可以有size()+1个元素啊……

一种实现：
capacity()始终>=size()+1。
data() 直接返回内部数组的地址。
c_str() 也返回这个数组的地址， 但返回之前将末尾填个0……

zylthinking

OwnWaterloo 发表于 2011-12-29 18:45
c_str() 返回一个数组， 保证有size()+1个元素， 前size()个元素是字符串内容（可能有0）， s.c_str() 是0  ...

好吧， 我承认是更好一些， 而且我之前也没想到这个办法

giantchen

回复 5# zylthinking


    你见过哪家的 std::string::c_str() 是这么实现的？

zylthinking

giantchen 发表于 2011-12-30 10:04
回复 5# zylthinking

我返回去仔细想了想， 发觉是被误导了：


string::c_str
public member function
const char* c_str ( ) const;
Get C string equivalent

Generates a null-terminated sequence of characters (c-string) with the same content as the string object and returns it as a pointer to an array of characters.

A terminating null character is automatically appended.

The returned array points to an internal location with the required storage space for this sequence of characters plus its terminating null-character, but the values in this array should not be modified in the program and are only guaranteed to remain unchanged until the next call to a non-constant member function of the string object.


string::data
public member function
const char* data() const;
Get string data

Returns a pointer to an array of characters with the same content as the string.

Notice that no terminating null character is appended (see member c_str for such a functionality).

The returned array points to an internal location which should not be modified directly in the program. Its contents are guaranteed to remain unchanged only until the next call to a non-constant member function of the string object.

看到以上时， 脑筋没转弯； 事后又忘记的差不多， 只记得有这么回事， 误以为是从源码看到的

chary8088

oh MGD
it is supposed that c_str() return the pointer of the array, which should not malloc a copy.

kkppccdd

C使用char[]保存字符串，以结束符表示字符串结尾。std::string加了数据缓冲区起始标志。