为什么首先要在strcat（）之前先使用strcpy（）？ [英] Why do i first have to strcpy() before strcat()?

问题描述

为什么这段代码会产生运行时问题：

Why does this code produce runtime issues:

char stuff[100];
strcat(stuff,"hi ");
strcat(stuff,"there");

但这不是吗？

char stuff[100];
strcpy(stuff,"hi ");
strcat(stuff,"there");

推荐答案

strcat 将查找null终止符，将其解释为字符串的结尾，然后在其中附加新文本，覆盖过程中的null终止符，并在连接末尾编写新的null终止符。

strcat will look for the null-terminator, interpret that as the end of the string, and append the new text there, overwriting the null-terminator in the process, and writing a new null-terminator at the end of the concatenation.

char stuff[100];  // 'stuff' is uninitialized

空终止符在哪里？ 东西未初始化，因此它可能以NUL开头，或者其中可能没有NUL。

Where is the null terminator? stuff is uninitialized, so it might start with NUL, or it might not have NUL anywhere within it.

在C ++，您可以执行以下操作：

In C++, you can do this:

char stuff[100] = {};  // 'stuff' is initialized to all zeroes

现在您可以执行strcat了，因为'stuff'是空终止符，因此它将附加到正确的位置。

Now you can do strcat, because the first character of 'stuff' is the null-terminator, so it will append to the right place.

在C语言中，您仍然需要初始化 stuff，这可以通过几种方法：

In C, you still need to initialize 'stuff', which can be done a couple of ways:

char stuff[100]; // not initialized
stuff[0] = '\0'; // first character is now the null terminator,
                 // so 'stuff' is effectively ""
strcpy(stuff, "hi ");  // this initializes 'stuff' if it's not already.

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