c - scanf 何时将 '\0' 附加到用户输入？

Question

我知道 scanf("%s",arr); 会自动将 '\0' 附加到用户输入中。但我以为也仅限于此。然而，即使 scanf("%[^\n]",arr); 也会附加一个 '\0'。(我知道这会扫描所有字符，直到到达换行符)。在这种情况下，会将 '\0' 添加到 '\n' 之后或 '\n' 之前。另外，我们如何确定何时以及何时不添加 '\0' ？我们如何扫描多个字符以形成字符数组而不是字符串？

Answer 1

Also how do we figure out when and when not '\0' will be appended?

如scanf是一个标准函数，我们从 C 标准中算出来。来自 C11 draft 7.21.6.2p12 :

s
... the corresponding argument shall be a pointer to the initial element of a character array large enough to accept the sequence and a terminating null character, which will be added automatically. ...

[
... the corresponding argument shall be a pointer to the initial element of a character array large enough to accept the sequence and a terminating null character, which will be added automatically. ...

还有更好看且常用于快速引用的 cppreference网站。

我强烈建议您永远不要使用 %s和%[没有指定“最大字段宽度”的数字(除非您知道可以使用它)。始终使用%<number>s和%<number>[ ，限制读取的字符数并防止溢出。所以总是:

char arr[20];
scanf("%19s", arr);

scanf这种方式是非常不安全的函数，读取字符串时很容易出现堆栈溢出。

How do we scan many characters to just form a character array and not a string?

我想你想要:

size_t fread(void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream);

The fread function reads, into the array pointed to by ptr, up to nmemb elements whose size is specified by size, from the stream pointed to by stream.

它将显示 nmemb尺寸元素size到ptr指向的内存。所以只是:

 char character_array[20];
 size_t number_of_chcaracter_read = fread(character_array, 20, 1, stdin);

它不会将终止空字节附加到 character_array .