字符串字面量\0表示什么？ [英] What does the symbol \0 mean in a string-literal?

问题描述

考虑以下代码：

char str[] = "Hello\0";

str数组的长度是多少，以0结尾多少？

What is the length of str array, and with how much 0s it is ending?

推荐答案

sizeof str 是7到5个字节，用于 Hello文本，外加显式NUL终止符，再加上隐式NUL终止符。

sizeof str is 7 - five bytes for the "Hello" text, plus the explicit NUL terminator, plus the implicit NUL terminator.

strlen（str）是5-五个 Hello

strlen(str) is 5 - the five "Hello" bytes only.

这里的关键是总是添加隐式nul终止符 -即使字符串文字恰好以<$结尾c $ c> \0 。当然， strlen 只是在第一个 \0 处停止-无法分辨出差异。

The key here is that the implicit nul terminator is always added - even if the string literal just happens to end with \0. Of course, strlen just stops at the first \0 - it can't tell the difference.

隐式NUL终止符规则有一个例外-如果您明确指定数组大小，则字符串将被截断以适合：

There is one exception to the implicit NUL terminator rule - if you explicitly specify the array size, the string will be truncated to fit:

char str[6] = "Hello\0"; // strlen(str) = 5, sizeof(str) = 6 (with one NUL)
char str[7] = "Hello\0"; // strlen(str) = 5, sizeof(str) = 7 (with two NULs)
char str[8] = "Hello\0"; // strlen(str) = 5, sizeof(str) = 8 (with three NULs per C99 6.7.8.21)

但是，它很少有用，并且容易错误计算字符串长度并最终以未终止的字符串结尾。在C ++中也禁止使用。

This is, however, rarely useful, and prone to miscalculating the string length and ending up with an unterminated string. It is also forbidden in C++.

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