user-0 提问: scanf 使用上的一些问题

回复:
user: user-1
content: 这里有关于scanf()的详解，是另一位博主的     https://bbs.csdn.net/topics/600546032

user: user-2
content: Format Specification Fields: scanf and wscanf FunctionsA format specification has the following form: %[*] [width] [{h | l | I64 | L}]type The format argument specifies the interpretation of the input and can contain one or more of the following:  White-space characters: blank (' '); tab ('\t'); or newline ('\n'). A white-space character causes scanf to read, but not store, all consecutive white-space characters in the input up to the next non–white-space character. One white-space character in the format matches any number (including 0) and combination of white-space characters in the input. Non–white-space characters, except for the percent sign (%). A non–white-space character causes scanf to read, but not store, a matching non–white-space character. If the next character in stdin does not match, scanf terminates. Format specifications, introduced by the percent sign (%). A format specification causes scanf to read and convert characters in the input into values of a specified type. The value is assigned to an argument in the argument list.The format is read from left to right. Characters outside format specifications are expected to match the sequence of characters in stdin; the matching characters in stdin are scanned but not stored. If a character in stdin conflicts with the format specification, scanf terminates, and the character is left in stdin as if it had not been read. When the first format specification is encountered, the value of the first input field is converted according to this specification and stored in the location that is specified by the first argument. The second format specification causes the second input field to be converted and stored in the second argument, and so on through the end of the format string. An input field is defined as all characters up to the first white-space character (space, tab, or newline), or up to the first character that cannot be converted according to the format specification, or until the field width (if specified) is reached. If there are too many arguments for the given specifications, the extra arguments are evaluated but ignored. The results are unpredictable if there are not enough arguments for the format specification. Each field of the format specification is a single character or a number signifying a particular format option. The type character, which appears after the last optional format field, determines whether the input field is interpreted as a character, a string, or a number.  The simplest format specification contains only the percent sign and a type character (for example, %s). If a percent sign (%) is followed by a character that has no meaning as a format-control character, that character and the following characters (up to the next percent sign) are treated as an ordinary sequence of characters, that is, a sequence of characters that must match the input. For example, to specify that a percent-sign character is to be input, use %%. An asterisk (*) following the percent sign suppresses assignment of the next input field, which is interpreted as a field of the specified type. The field is scanned but not stored.

user: user-2
content: #include <stdio.h> #include <string.h>   int main(){     char str1[30] = {0};     char str2[30] = {0};     char str3[30] = {0};     char str4[30] = {0};       printf("first:\n");      scanf("%[a-zA-Z]", str1);            scanf("%s", str2);                   printf("str1 = %s\n", str1);          printf("str2 = %s\n", str2);           printf("\nsecond:\n");     rewind(stdin);     scanf("%[a-zA-Z]", str3);             scanf("%s", str4);              printf("str3 = %s\n", str3);     printf("str4 = %s\n", str4);       return 0; }

user: user-0
content: 那是每次使用 scanf 后都要清除缓冲区吗？为什么我连续使用两个scanf("%s", str1);  scanf("%s", str2); 打印出来都很正常？

user: user-3
content: 代码一样但是环境不同啊。第一次结束之后输入缓冲区里残留着一个换行符，于是它干扰了第二次的输入。

user: user-0
content: 我还是不明白，第一次输入不是被 str2 给接收了吗？为什么会还会留到 str3 接收换行呢？

user: user-3
content: 默认的%s会接受并忽略前置白空格，并在前瞻到后置白空格的时候停下，并不接受它。 而你的正则式显然是另外一个脾气。