C语言 使用 `scanf()` 读取逗号分隔的输入
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read comma-separated input with `scanf()`
提问by Moonlit
I have the following input:
我有以下输入：
AG23,VU,Blablublablu,8
IE22,VU,FooBlaFooBlaFoo,3
and so on...
I want it to "parse" with scanf()using some code like this:
我希望它scanf()使用这样的代码来“解析” ：
char sem[5];
char type[5];
char title[80];
int value;
while(scanf("%s,%s,%s,%d", sem, type, title, &value) == 4) {
//do something with the read line values
}
But the execution of the code gives me: illegal instruction
但是代码的执行给了我： illegal instruction
How would you read a comma-separated file like this?
您将如何读取这样的逗号分隔文件？
回答by hmjd
The comma is not considered a whitespace character so the format specifier "%s"will consume the ,and everything else on the line writing beyond the bounds of the array semcausing undefined behaviour. To correct this you need to use a scanset:
逗号不被视为空白字符，因此格式说明符"%s"将消耗,和 行上的所有其他内容，写入超出数组边界，sem导致未定义行为。要纠正此问题，您需要使用扫描集：
while (scanf("%4[^,],%4[^,],%79[^,],%d", sem, type, title, &value) == 4)
where:
在哪里：
%4[^,]means read at most four characters or until a comma is encountered.
%4[^,]表示最多读取四个字符或直到遇到逗号。
Specifying the width prevents buffer overrun.
指定宽度可防止缓冲区溢出。
回答by Andrés AG
The problem that you are having is because when you say
你遇到的问题是因为当你说
scanf("%s,%s,%s,%d", sem, type, title, &value)
what happens is that you are trying doing is that you are fitting all the line into the first string which is just 5 characters. Therefore the sem[5]overflows, and soes all sorts of funny things. To avoid this problem, I tried using the expression %[^,], but it is not quite working. The best bet is to use something like
发生的情况是，您正在尝试将所有行放入第一个只有 5 个字符的字符串中。因此，sem[5]溢出，soes各种有趣的事情。为了避免这个问题，我尝试使用表达式%[^,]，但它不太有效。最好的办法是使用类似的东西
while(scanf("%s%c%s%c%s%c%d", sem, &ch, type, &ch, title, &ch, &value) != EOF)
Then you can just discard the ch. However bear in mind that is better to use other functions to reading input such as getchar(), and things like that, which are much faster and safer in some sense.
然后你可以丢弃ch. 但是请记住，最好使用其他函数来读取输入，例如getchar()，以及类似的东西，它们在某种意义上更快更安全。
