我的sscanf格式有什么问题 [英] What is wrong with my sscanf format

问题描述

我正在这里处理c中的表单数据。

I'm trying to deal with form data in c here.

fgets(somedata, bufferone, stdin);  

如果我printf'somedata'，我得到：

if I printf 'somedata', I get:

username=John&password=hispass123

现在当我尝试使用

char usr[100], pass[100];
sscanf(somedata, "username=%s&password=%s", usr, pass);
printf("Content-type: text/html\n\n");
printf("%s is value 1\n", usr);
printf("%s is value 2\n", pass);

比我得到的

John&password=hispass123 is value 1
?? is value 2

我怀疑，第一个调用读取的是空终止符，然后第二个调用溢出之类的。

I suspect, the first call reads up to the null-terminator, and then second call overflows or something.

所以我需要有关格式的帮助。另外，在这种情况下sscanf函数是最佳选择吗？我正在尝试从邮件正文中获取2个字符串（由html表单通过stdin发送）。

So I need help with the format. Also, is sscanf function the best choice in this scenario? I'm trying to obtain 2 strings from the message body (sent via stdin by the html form).

推荐答案

％s 是贪婪的。它拾取路径中不是空格字符的所有内容。将其更改为使用％[^&] 。

"%s" is greedy. It picks up everything in its path that is not a whitespace character. Change it to use "%[^&]".

sscanf(somedata, "username=%[^&]&password=%s", usr, pass);

％[^&] 部分格式说明符的将会提取不是不是字符& 的任何字符。当遇到& 时，它将停止提取。

The %[^&] part of the format specifier will extract any character that is not the character &. It will stop extracting when it encounters a &.

为使代码更健壮，请始终检查返回值 sscanf / fscanf 。

To make your code a bit more robust, always check the return value of sscanf/fscanf.

int n = sscanf(somedata, "username=%[^&]&password=%s", usr, pass);
if ( n != 2 )
{
   // There was a problem reading the data.
}
else
{
   // Reading was successful. Use the data.
   printf("Content-type: text/html\n\n");
   printf("%s is value 1\n", usr);
   printf("%s is value 2\n", pass);
}

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