std::string你也許不知道的秘密

OwnWaterloo

c_str() 返回一個數(shù)組， 保證有size()+1個元素， 前size()個元素是字符串內(nèi)容（可能有0）， s.c_str()[size()] 是0 。
而data() 返回一個數(shù)組。 如果size()>0 則保證有size()個元素， 前size個元素是字符串內(nèi)容， 沒說它不可以有size()+1個元素啊……

一種實現(xiàn)：
capacity()始終>=size()+1。
data() 直接返回內(nèi)部數(shù)組的地址。
c_str() 也返回這個數(shù)組的地址， 但返回之前將末尾填個0……

zylthinking

OwnWaterloo 發(fā)表于 2011-12-29 18:45
c_str() 返回一個數(shù)組， 保證有size()+1個元素， 前size()個元素是字符串內(nèi)容（可能有0）， s.c_str() 是0  ...

好吧， 我承認(rèn)是更好一些， 而且我之前也沒想到這個辦法

giantchen

回復(fù) 5# zylthinking


    你見過哪家的 std::string::c_str() 是這么實現(xiàn)的？

zylthinking

giantchen 發(fā)表于 2011-12-30 10:04
回復(fù) 5# zylthinking

我返回去仔細(xì)想了想， 發(fā)覺是被誤導(dǎo)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.

看到以上時， 腦筋沒轉(zhuǎn)彎； 事后又忘記的差不多， 只記得有這么回事， 誤以為是從源碼看到的

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，以結(jié)束符表示字符串結(jié)尾。std::string加了數(shù)據(jù)緩沖區(qū)起始標(biāo)志。