C語言中既然""與空格『 』是不一樣的，那為什麼在字元串問題中，scanf中還不能讀入空格？

例如字元串"hello world"，用scanf以%s格式輸入，只能輸出"hello"，字元串是以『』作為結尾，而『 』!=""。

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Reading Undelimited strings

scanf Width Specification

To read strings not delimited by whitespace characters, a set of characters in brackets ([ ]) can be substituted for the s (string) type character. The set of characters in brackets is referred to as a control string. The corresponding input field is read up to the first character that does not appear in the control string. If the first character in the set is a caret (^), the effect is reversed: The input field is read up to the first character that does appear in the rest of the character set.

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因為是這樣設計的。

如果有讀取空格的需求，可以參考如下代碼。

#include &
int main()
{
char str[128];
scanf( "%[^
]", str );
printf( "%s
", str );
return 0;
}


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這不是說明空格與等價，而是由於C語言的緩衝機制，scanf讀取數據不是從鍵盤直接讀取，因為鍵盤是字元型輸入設備，且它是中斷方式來被操作系統控制，所以這些IO設備存取速率及其低下，而內存是塊設備，讀取速度非常快，因此引入緩衝區機制來緩衝IO設備與內存的數據交換，scanf也是從緩衝區地區，而scanf函數是把空格作為緩衝區數據的分隔符，每遇到一個空格，則表示當前一段數據為可用數據被scanf讀取，而不是空格表示字元結束而被讀入

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