std :: string :: assign与std :: string :: operator = [英] std::string::assign vs std::string::operator=

问题描述

我很早以前就用Borland C ++编写代码，现在我正试图理解新（对我）C + 11（我知道，我们在2015年，有一个c + 14 ...但是我'正在从事C ++ 11项目）

I coded in Borland C++ ages ago, and now I'm trying to understand the "new"(to me) C+11 (I know, we're in 2015, there's a c+14 ... but I'm working on an C++11 project)

现在，我有几种方法可以给字符串赋值。

Now I have several ways to assign a value to a string.

#include <iostream>
#include <string>
int main ()
{
  std::string test1;
  std::string test2;
  test1 = "Hello World";
  test2.assign("Hello again");

  std::cout << test1 << std::endl << test2;
  return 0;
}

它们都起作用。我从 http://www.cplusplus.com/reference/string/string/assign了解到/ ，还有另一种使用 assign 的方法。但是对于简单的字符串分配，哪个更好？我必须用8个std：string填充100+个结构，而我正在寻找最快的机制（我不关心内存，除非有很大的不同）

They both work. I learned from http://www.cplusplus.com/reference/string/string/assign/ that there are another ways to use assign . But for simple string assignment, which one is better? I have to fill 100+ structs with 8 std:string each, and I'm looking for the fastest mechanism (I don't care about memory, unless there's a big difference)

推荐答案

两者都同样快，但是 = ... 更清晰。

Both are equally fast, but = "..." is clearer.

但是，如果您确实想要快速，请使用 assign 并指定大小：

If you really want fast though, use assign and specify the size:

test2.assign("Hello again", sizeof("Hello again") - 1); // don't copy the null terminator!
// or
test2.assign("Hello again", 11);

这样，只需要进行一次分配即可。 （您还可以预先 .reserve（）足够的内存来获得相同的效果。）

That way, only one allocation is needed. (You could also .reserve() enough memory beforehand to get the same effect.)

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