不同的scanf格式之间的差异 [英] Difference between different scanf formats

问题描述

我正在准备通过阅读教科书来编程学校。这个问题我不明白，教科书也没有给出答案。

PS：我在网上学了一些C ++ / C＃通过适当的教程编程类，所以我挣扎着一些概念。

问：对于以下每对scanf格式字符串，表示
两个字符串是否相等。如果他们不是，显示
如何区分他们。

A）％d与％d

B）％d-％d-％d与％d - ％d - ％d

C）％f与％f

D）％f，％f vs ％f，％f

首先，我甚至不明白问题在问什么。教科书是否意味着这两个字符串是否相等？

如果是的话，有人可以解释一下这些差异，并告诉我他们是如何区分的吗？解决方案 c>首先：％d vs ％d，它们是 scanf（）的等效格式字符串。

将执行以下操作。它永远不会失败。

1）扫描并放弃（跳过）可选的空格。

2）读取非空白或文件结束后，如果没有（EOF），读取的最后一个字符被放回到 stdin 。

％ d本身会尝试3件事（可能会失败）

1）扫描并放弃（跳过）可选的空白区域

2）扫描并放弃转换表示十进制整数的数字文本。

3）读取非数字文本或文件结束后，如果不是（EOF），则读取的最后一个字符被放回到 stdin 。

％d这与刚刚用％d执行第二个操作的结果是一样的。 $ b

用 * scanf（）说明符注意：

输入空格字符（由<$ c除非规范包含 [， c 函数）被跳过， ，或 n 说明符。 C11§7.21.6.28

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B ， C ， D 差异？

鼠标悬停提示1：

A 在 scanf（）说明符之前，除了上面提到的3之外，它是一个等效的scanf（）格式，没有它。

鼠标悬停提示2：

/ b>

鼠标悬停提示3：

考虑输入：

123 -456-789

123.456 x接下来要读取的字符是什么？

％d-％d-％d vs ％d - ％d - ％d

C）％f与％f

D）％f，％f与％f，％f

回答：

I'm currently prepping myself for programming school by going through the textbook. There's this particular question which I don't understand and the textbook doesn't give the answer.

PS: I've learned some C++/C# online, but never go through proper-taught programming classes, so I'm struggling with some of the concepts.

Q: For each of the following pairs of scanf format strings, indicate whether or not the two strings are equivalent. If they are not, show how they can be distinguished.

A) "%d" versus " %d"
B) "%d-%d-%d" versus "%d -%d -%d"
C) "%f" versus "%f "
D) "%f,%f" versus "%f, %f"

First off, I don't even understand what the question is asking. What does the textbook mean by whether or not the 2 strings are 'equivalent'?

If they are, could someone explain the differences and possibly show me how they can be distinguished?

解决方案

Let us try A first: "%d" versus " %d", they are equivalent format strings for scanf().

" " will do the following. It never fails.
1) Scan and discard (skip) optional white-space.
2) After reading a non-white-space or end-of-file, if not (EOF), the last character read is put back into stdin.

"%d" itself will attempt 3 things (It can fail)
1) Scan and discard (skip) optional white-space.
2) Scan and convert numeric text representing a decimal integer.
3) After reading a non-numeric text or end-of-file, if not (EOF), the last character read is put back into stdin.

" %d" does both the above. It is the same result of just doing the 2nd with "%d".

With *scanf() specifiers note:

Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a [, c, or n specifier. C11 §7.21.6.2 8

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B, C, D differences?

Mouse over for hint 1:

A " " before a scanf() specifier, except the 3 noted above, is an equivalent scanf() format as without it.

Mouse over for hint 2:

Only 1 of 3 equivalent.

Mouse over for hint 3:

Consider inputs:
"123 -456-789"
"123.456 x" What is the next character to be read?

B) "%d-%d-%d" versus "%d -%d -%d"
C) "%f" versus "%f "
D) "%f,%f" versus "%f, %f"

Answer:

Awww, Do you really want to be given the answer?

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