使用 strstr 查找 substring 的所有实例导致奇怪的字符串格式
[英]Using strstr to find all instances of substring results in weird string formatting
问题描述
I'm making a web scraper and i'm at the point where I need to parse the incoming data.
我正在制作一个 web 刮板，我正处于需要解析传入数据的位置。 Everything was going fine until I had to find all instances of a substring in a string.一切都很顺利，直到我不得不在字符串中找到 substring 的所有实例。 I was able to get something working but it doesn't give me the full string I want (which is a full <p></p> tag).我能够得到一些工作，但它没有给我我想要的完整字符串（这是一个完整的<p></p>标签）。
done = 0;
while (done == 0) {
if ((findSpan = strstr(serverResp, "<p")) != NULL) {
printf("%s\n", findSpan);
if ((findSpanEnd = strstr(findSpan, "</p>")) != NULL) {
strcpy(serverResp, findSpanEnd);
strcpy(findSpanEnd+4, "");
printf("after end tag formattng %s\n", findSpan);
}
} else {
done = 1;
}
}
After end tag formatting should give me a result along the lines of <p>insert text here</p> but instead, I get something like this:结束标记格式化后应该给我一个类似于<p>insert text here</p>的结果，但相反，我得到的是这样的：
<p>This should be printed</p>
<h3>ignore</h3>
<p>and so should this</p>
</body>
</html>
after end tag formatting <p>This should be printed</p>
<h3>ignore</h3>
<p>and so should this</p>
</body>
</html>
after end tag formatting dy>
</html>
The site's code looks like this:该网站的代码如下所示：
<!DOCTYPE html>
<html>
<head></head>
<body>
<h1>ignore this</h1>
<p>This should be printed</p>
<h3>ignore</h3>
<p>and so should this</p>
</body>
</html>
1 个解决方案
解决方案1
1 已采纳 2022-02-26 01:26:24
if ((findSpanEnd = strstr(findSpan, "</p>")) != NULL) {
strcpy(serverResp, findSpanEnd);
This makes no sense.这是没有意义的。 strstr finds "</p>" as requested; strstr按要求查找"</p>" ； however you can't pass that to strcpy like that.但是你不能像那样将它传递给strcpy 。 strstr doesn't allocate a new string at all; strstr根本不分配新字符串； it only returns the location within the old one.它只返回旧位置中的位置。
A routine to print out all <p> tags would look like this (note that this assumes no nested <p> tags):打印出所有<p>标签的例程如下所示（请注意，这假定没有嵌套的<p>标签）：
for (char *ptr = serverResp; ptr = strstr(ptr, "<p");)
{
char *finger = strchr(ptr, '>');
if (!finger) break;
++finger;
ptr = strstr(finger, "</p>");
if (!ptr) {
fwrite(finger, 1, strlen(finger), stdout);
} else {
fwrite(finger, 1, ptr - finger, stdout);
}
fputs("\r\n", stdout);
}
The technique: the call to strstr in the for loop locates the next <p> tag, strchr finds the end of it, then another strstr finds the closing </p> Because the return pointers are into the originating string, we use fwrite instead of printf to produce output.技术：for 循环中对strstr的调用定位下一个<p>标记， strchr找到它的结尾，然后另一个strstr找到结束</p>因为返回指针指向原始字符串，所以我们改用fwrite printf生成 output。
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