strlen的C和C ++：它是如何工作的？ [英] strlen in C and C++ : how does it work?

问题描述

如何的strlen（）内部工作？以及是否有任何固有缺陷的功能？

How does strlen() work internally? And are there any inherent bugs in the function?

推荐答案

的strlen 通常是通过在一个字符串，直到 \\ 0计数的人物作品字符被发现。一个典型的实现将是：

strlen usually works by counting the characters in a string until a \0 character is found. A canonical implementation would be:

size_t strlen (char *str) {
    size_t len = 0;
    while (*str != '\0') {
        str++;
        len++;
    }
    return len;
}

有在功能没有固有的缺陷，它的工作原理完全一样记录。

There is no inherent bug in the function, it works exactly as documented.

这并不是说就没有问题，即：

That's not to say it doesn't have problems, to wit:

• 如果你传递一个串不具有 \\ 0 末，你可能会碰到的问题，但是从技术上来说，这不是一个C字符串< SUP>（一），这是你自己的错。


• 您不能把 \\ 0 在字符串中的字符，但再次，它不会在这种情况下，C字符串。


• 这不是最有效的方式 - 你可以存储一个长度可达前面，这样你可以得到的长度更快

• if you pass it a "string" that doesn't have a \0 at the end, you may run into problems but technically, that's not a C string ^(a) and it's your own fault.
• you can't put \0 characters in your string but, again, it wouldn't be a C string in that case.
• it's not the most efficient way - you could store a length up front so you could get the length much quicker.

但这些都不是错误，他们只是一个设计决策的后果。

But none of those are bugs, they're just consequences of a design decision.

另请参见由Joel Spolsky的这个优秀的文章，他在那里讨论了各种字符串格式及其特征，包括普通的C字符串，字符串帕斯卡尔和两者的结合，空终止字符串帕斯卡，虽然他有一个更，应我们说，他们多彩一词： - ）

See also this excellent article by Joel Spolsky where he discusses various string formats and their characteristics, including normal C strings, Pascal strings and the combination of the two, null terminated Pascal strings, though he has a more, shall we say, "colorful" term for them :-)

^（一） C字符串被定义为随后是一系列的非终止字符（即比其他任何\\ 0 ）终止符。因此，这一定义不允许的顺序和序列中都嵌入终结没有这样一个终止符。

^(a) A C string is defined as a series of non-terminator characters (ie, any other than \0) followed by that terminator. Hence this definition disallows both embedded terminators within the sequence and sequences without such a terminator.

或者，把它更简洁（根据ISO标准）：

Or, putting it more succinctly (as per the ISO standard):

一个字符串是由终止字符的连续序列与包括第一个空
  性格。

A string is a contiguous sequence of characters terminated by and including the first null character.

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