how to use strstr

[JeanC]

Hello,

This code crashes with segfault


QString MainWindowImpl::getIp(QString line)
{
static char ip[1000], s[1000];
strcpy(s, line.toLocal8Bit().constData());
char *p1 = strstr(s, "client ") + 7, *p2 = ip;
while (*p1 && *p1 != ']')
*p2++ = *p1++;
*p2 = 0;
return ip;


If I change the line with strstr to:


char *p1 = s + 7, *p2 = ip;

all is well..

I know I can do things the qt way but I want to be portable with plain c strings.
Thanks.

[Ginsengelf]

I know I can do things the qt way but I want to be portable with plain c strings.

But you start with a QString anyway, so why not stay in the Qt realm?

Ginsengelf

[JeanC]

That is explained in the post.


But you start with a QString anyway, so why not stay in the Qt realm?

Ginsengelf

[bunjee]

I'd use strncpy to copy the exact length of the string.

And don't forget to add a NULL in the end, otherwise strstr won't likely work.

[JeanC]

int len = line.length();
strncpy(s, line.toLocal8Bit().constData(), len);
s[len] = 0;
char *p1 = strstr(s, "client ") + 7, *p2 = ip;


Still segfaults. I would have been very surprised if that was the solution, a normal strcpy wouldn't work and a strncpy would?

[bunjee]

did you try replacing


line.toLocal8Bit().constData()

by


line.toStdString().c_str()

Is it still crashing on that line :
char *p1 = strstr(s, "client ") + 7, *p2 = ip; ?
why do you declare
static char ip[1000], s[1000]; as static ?

[JeanC]

line.toStdString().c_str()

Just tried. Same result. From the posts I've read the only safe way is with those calls I used, as I understood it, all the rest leaves dangling pointers.



why do you declare
static char ip[1000], s[1000]; as static ?


Oops that's typo.

I thought Qt was about c++, I wonder what it takes to have it use charpointers, maybe some voodoo? Sigh. I don't understand why this is so hard. There's tons of c code out there, I have still useful code I wrote 25 years ago, I'm not gonna qchar or qbytearray all that. Sorry for the rant.

[wysota]

I know I can do things the qt way but I want to be portable with plain c strings.

How does using strstr on a string ripped from QString make you "portable with plain c strings"?

I'd check strstr() result for NULL and divide those statements separated by commas into two (or even three if you consider the "+7" part) real statements if I were you...

[JeanC]

Hey wysota,


I'd check strstr() result for NULL

I don't even have to try out the code, not checking for NULL from strstr is the error.

That is basic stuff, how can I forget that, I'm getting too old for this, I have to try another hobby like go fishing or so. :)