std :: istringstream从std :: string不复制 [英] std::istringstream from std::string without copying

问题描述

我一直在使用这个：

  ifstream in（file.txt）
 string line; 
 getline（in，line）; 
 istringstream iss（line）; 
 ... 
  

我想避免不必要的复制，以提高性能，所以我尝试：

  ifstream in（huge_line。文本）; 
 string line; 
 getline（in，line）; 
 istringstream ss; 
 ss.rdbuf（） - > pubsetbuf（const_cast< char *>（line.c_str（）），line.size（））; 
 ... 
  

似乎做了这项工作）。我的问题是，这是安全给定的const_cast？
我的意思是，只要我使用istrinstream，内部缓冲区不应该被istringstream类写入，所以ss变量应该保持在一个有效的状态，只要行变量有效，

$ const_cast 是安全的，因为底层的 std :: string 的缓冲区不是 const 。是的，只要行没有过期，而 ss 正在读取，你的程序应该是罚款。 / p>

I've been using this:

ifstream in("file.txt")
string line;    
getline(in,line);
istringstream iss(line);
...

for some simple parsing. I would like to avoid unnecessary copying in order to improve performance so I tried:

ifstream in("huge_line.txt");
string line;
getline(in,line);
istringstream ss;
ss.rdbuf()->pubsetbuf(const_cast<char*>(line.c_str()), line.size());
...

and it seems to do the job (significantly improve performance, that is). My question is, is this safe given the const_cast? I mean, as long as I'm working with an istrinstream, the internal buffer should never get written to by the istringstream class, so the ss variable should remain in a valid state as long as the line variable is valid and unchanged, right?

解决方案

The const_cast is safe, because the underlying buffer of std::string is not const. And yes, as long as line does not expire while ss is being read from, your program should be fine.

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