在 scanf() 中使用与号 [英] Using an ampersand in scanf()

问题描述

当我编译 scanf("%s", &var); 时，gcc 发回警告:

When I compile scanf("%s", &var);, gcc sends back a warning:

warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[20]’

然而，当我编译 scanf("%s", var); 时，没有应用警告.两段代码工作和我正在阅读的书都特别提到要使用和号，但即使在某些示例中也没有.

however when I compile scanf("%s", var);, no warning is applied. Both pieces of code work and the book I am reading specifically says to use the ampersand, but even it doesn't in some of the examples.

我的问题是，即使书中没有指定，我是否应该继续使用&符号?

My question is, should I continue to use the ampersand, even when the book doesn't specify?

推荐答案

根据您发布的内容 var 是一个字符数组.在这种情况下，您不需要&符号，只是名称 var 将根据需要计算为 (char *).

From what you've posted var is a char array. In that case, you don't need the ampersand, just the name var will evaluate to a (char *) as needed.

详情:

scanf 需要一个指向将存储输入的变量的指针.在字符串的情况下，您需要一个指向内存中字符数组的指针，该数组足够大以存储读入的任何字符串.当您声明诸如 char var[100] 之类的内容时，您为100 个 char s，其中 var[0] 指的是第一个字符，var[99] 指的是第 100 个字符.数组名称本身的计算结果与 &var[0] 完全相同，它是指向序列第一个字符的指针，正是 scanf 所需要的.所以你需要做的就是 scanf("%s", var);，但要注意 scanf 不对输入字符串施加大小限制，所以如果用户输入一个 101 长度的字符串，你将有一个缓冲区溢出，这将导致错误，甚至更糟的是，安全问题.更好的选择通常是 fgets允许输入字符串的大小限制.

scanf needs a pointer to the variable that will store input. In the case of a string, you need a pointer to an array of characters in memory big enough to store whatever string is read in. When you declare something like char var[100], you make space for 100 chars with var[0] referring to the first char and var[99] referring to the 100th char. The array name by itself evaluates to exactly the same thing as &var[0], which is a pointer to the first character of the sequence, exactly what is needed by scanf. So all you need to do is scanf("%s", var);, but be aware that scanf does not enforce size constraints on input strings, so if the user inputs a 101 length string your will have a buffer overrun, which will result in bugs or, even worse, security problems. The better choice is generally fgets which does allow size constraints for input strings.

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