local string always corrupt

Christian Ehrlicher · wrote on 22 Oct 2018, 06:02

You do not check if ijl.toLocal8Bit() is shorter than 40 bytes.

rohit713 · J jsulm 22 Oct 2018, 06:01

@jsulm before strcpy it contain "risk" after calling strcpy it gives not accesible.

jsulm · 22 Oct 2018, 06:06

@rohit713 As @Christian-Ehrlicher said: you implemented a nice example for stack overflow :-)
You should use strncpy.

aha_1980 · J jsulm 22 Oct 2018, 06:04

@jsulm

Even better: qstrncpy ;)

rohit713 · 22 Oct 2018, 06:07

@jsulm i also tried strncpy but the same problem occurs .

jsulm · 22 Oct 2018, 06:12

@rohit713 Can you show how you used strncpy?

rohit713 · J jsulm 22 Oct 2018, 06:07

This post is deleted!

rohit713 · 22 Oct 2018, 06:16

@jsulm strncpy(pr,ijl.toLocal8Bit().data(),ijl.length());

jsulm · 22 Oct 2018, 06:16

@rohit713 This is same stack overflow as before...

rohit713 · 22 Oct 2018, 06:17

@jsulm can u share the stack overflow link

jsulm · wrote on 22 Oct 2018, 06:17

@rohit713 What link? Think about what will happen if ijl.toLocal8Bit().data() is longer than pr.

aha_1980 · 22 Oct 2018, 06:24

@rohit713

Use qstrncpy(pr, ijl.toLocal8Bit().constData(),sizeof(pr));

rohit713 · 22 Oct 2018, 06:43

@aha_1980 same problem occur with qstrncpy.

jsulm · wrote on 22 Oct 2018, 06:43

@rohit713 So, you used exactly this line:

qstrncpy(pr, ijl.toLocal8Bit().constData(),sizeof(pr));

?
Use debugger and step by step execution to see what happens.

ambershark · wrote on 24 Oct 2018, 04:47

@rohit713 said in local string always corrupt:

@jsulm can u share the stack overflow link

Lol he means an actual stack overflow, i.e. you have the potential for overrunning the memory in your buffer with how you used strcpy and strncpy. Not stackoverflow.com the website. ;)

You also don't leave room for the null terminator (or copy it). So you're resulting string if used in any string function is almost guaranteed to crash, at least in release mode. I don't think either of these are your actual issue though.

before strcpy it contain "risk" after calling strcpy it gives not accesible.

What does that mean? What gives not accessible? The debugger? If it was truly not accessible then it would cause a crash. After it's "not accessible" can you output it via qdebug? My guess here is QString is just reallocating it's internal memory and you are now watching the wrong memory location.

If you could show us the backtrace from the crash log that would help. Like I said I tested the code and it worked. I realize Qt5 is different that 4, but that string memory should be good during your copy even in Qt4. It worked in 5 I suspect if I had easy access to Qt4 it would work there too. Can you give us more information on what the actual problem is? "Not accessible" doesn't mean much.