如何获得一个格式化的std :: string在c ++没有长度限制 [英] How to get a formatted std::string in c++ without length liminations

问题描述

在c ++中这是最好的方法（简短，使用标准库和易于理解）：

What is the best way (short, using standard libraries and easy to understand) to do this in c++:

std::string s = magic_command("%4.2f", 123.456f)

• 没有长度限制（char s [1000] = ...）


• 其中％4.2f是任何c格式字符串（例如printf） li>
  
  • without length limitations (char s[1000] = ...)
  • where "%4.2f" is any c format string (which would be given to printf for example)

  我注意到snprintf malloc组合在

  I am aware of the snprintf malloc combo suggested for pure c in

  a href =http://stackoverflow.com/questions/1854353/writing-formatted-data-of-unknown-length-to-a-string-c-programming>将未知长度的格式化数据写入字符串（C编程）

  writing formatted data of unknown length to a string (C programming)

  但是有更好，更简洁的方法来使用c ++吗？

  but is there a better, less verbose, way to do this with c++?

  我也知道

  将浮点数转换为c ++中的std :: string

  但我想传递ac格式字符串作为％4.2f，我找不到一个办法这样做与ostringstream。

  but I want to pass a c format string such as "%4.2f", and I could not find a way to do this with ostringstream.

  推荐答案

  因为似乎没有真正标准的方式做我想要的，我会投票你所有，并接受我自己的总结行动方案：

  All answers given are good since there seems to be no really standard way of doing what I want, I'll vote you all up, and accept my own sum up course of action:

  
  
  • 如果字符串足够短，可以手动估计它的大小，做它，乘以你的估计4，并静态分配。
  
  
  • 如果你可以逃脱stringstream + setprecision，做它，因为它是标准的
  
  
  • 如果不是，你愿意写和包括基于snprintf /检查溢出/动态分配的短助手函数，做它，并把它进入您的项目utils文件
  
  
  • 总是考虑哪个依赖对您的项目限制较少（也许您已经在使用其中的一个）：
    
    
    
    • 如果boost限制较少，请使用Boost.Format
    
    
    • 如果GNU / BSD扩展限制较少，请使用asprintf
    
    
    • if the string is short enough to estimate its size by hand, do it, multiply your estimative by 4, and allocate it statically.
    • if you can get away with stringstream + setprecision, do it since it is standard
    • if not, and you are willing to write and include a short helper function based on snprintf/check overflow/dynamic allocation, do it and put it into your project "utils" file
    • finnally consider which dependency is less restrictive for your project (maybe you are already using one of them):
      • if boost is less restrictive, use Boost.Format
      • if GNU/BSD extensions are less restrictive, use asprintf

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