Using strstr to find all instances of substring results in weird string formatting-CodePudding

I'm making a web scraper and i'm at the point where I need to parse the incoming data. Everything was going fine until I had to find all instances of a substring in a string. I was able to get something working but it doesn't give me the full string I want (which is a full  tag).

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 insert text here but instead, I get something like this:

        <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:

<!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>

CodePudding user response：

        if ((findSpanEnd = strstr(findSpan, "</p>")) != NULL) {
            strcpy(serverResp, findSpanEnd);

This makes no sense. strstr finds "" as requested; however you can't pass that to strcpy like that. strstr doesn't allocate a new string at all; it only returns the location within the old one.

A routine to print out all  tags would look like this (note that this assumes no nested  tags):

    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  tag, strchr finds the end of it, then another strstr finds the closing  Because the return pointers are into the originating string, we use fwrite instead of printf to produce output.