问题描述
我需要在C＃项目中使用C库。我该怎么办？
I need to use the C library in a C# project. How can I do?
更具体地说：出于效率考虑，我需要使用函数从字符串中提取双精度值（例如 9.63074,9.63074 -5.55708e-006 0，0 1477.78）。如果您对如何优化此操作有任何建议，请不要害羞，但主要问题仍然是标题指定的问题。
To be more specific: for reasons of efficiency I need to use the strtod function to extract double values from a string (like this "9.63074,9.63074 -5.55708e-006 0 ,0 1477.78"). If you have suggestions about how to optimize this operation do not be shy, but the main question remains that specified by title.
推荐答案
我认为p /调用 strtod 不可能比纯C＃解决方案更有效。在托管/非托管转换中会产生开销，我认为这对于 strtod 这样琐碎的事情来说意义重大。我自己会使用C＃令牌生成器，并结合 double.Parse 。
I think it very unlikely that p/invoking to strtod would be more efficient than a pure C# solution. There is an overhead in managed/unmanaged transitions and I would think that would be significant for something as trivial as strtod. Myself I would use a C# tokenizer, combined with double.Parse.
最简单的C＃令牌生成器是 String.Split（）产生以下例程：
The simplest C# tokenizer is String.Split() which yields this routine:
static List<double> getValues(string str)
{
List<double> list = new List<double>();
foreach (string item in str.Split(default(Char[]), StringSplitOptions.RemoveEmptyEntries))
list.Add(double.Parse(item));
return list;
}
但是，因为我喜欢p / invoke，这是从C＃调用 strtod 的方式，请记住，我建议您不要在实际代码中使用此方法。
However, since I enjoy p/invoke, here's how you would call strtod from C#, bearing in mind that I recommend you don't use this approach in real code.
[DllImport(@"msvcrt.dll", CallingConvention=CallingConvention.Cdecl)]
static extern double strtod(IntPtr str, ref IntPtr endptr);
您可以这样称呼它：
IntPtr str = Marshal.StringToHGlobalAnsi(inputStr);
IntPtr endptr = IntPtr.Zero;
double val = strtod(str, ref endptr);
Marshal.FreeHGlobal(str);
我将字符串作为 IntPtr ，因为您将反复调用 strtod 以遍历整个缓冲区。我没有在这里显示出来，但是如果您要使用 endptr 的话，就需要按照我的说明进行操作。
I'm passing the string as an IntPtr because you would be calling strtod repeatedly to walk across the entire buffer. I didn't show that here, but if you are going to make any use of endptr then you need to do it as I illustrate.
当然，要有效地远程使用 strtod ，您需要访问全局 errno 变量。您需要处理全局变量的事实应该足以警告您这是龙。而且，通过 errno 提供的错误报告非常有限。但是，如果需要，它在这里：
Of course, to use strtod remotely effectively you need to gain access to the errno global variable. The very fact that you need to deal with a global variable should be warning enough that here be dragons. What's more, the error reporting offered through errno is exceedingly limited. However, if you want it, here it is:
[DllImport(@"msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
static extern int _get_errno();
最后一点。您建议的输入字符串为
One final point. Your suggested input string is
"9.63074,9.63074 -5.55708e-006 0 ,0 1477.78"
，但由于虚假逗号， strtod 不会对此进行标记。
but strtod won't tokenize that because of the spurious commas.
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