local string always corrupt

[rohit713]

@mrjj ijl is qstring which is pass as an parameter in function abc ().

[rohit713]

@jsulm value of ijl string which is passed in function abc().

[rohit713]

@ambershark yes its work fine in qt 5 but my problem occur in qt 4 .ijl is coruupetd debugger shows the locale value not accesible while we copy this to pr its crash .

[jsulm]

@rohit713 But what do you mean by "not accessible"? Was it accessible before strcpy?
Note this (from http://doc.qt.io/qt-5/qstring.html#toLocal8Bit):
"The returned byte array is undefined if the string contains characters not supported by the local 8-bit encoding."

[Christian Ehrlicher]

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

[rohit713]

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

[jsulm]

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

[aha_1980]

@jsulm

Even better: qstrncpy ;)

[rohit713]

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

[jsulm]

@rohit713 Can you show how you used strncpy?

[rohit713]

This post is deleted!

[rohit713]

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

[jsulm]

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

[rohit713]

@jsulm can u share the stack overflow link

[jsulm]

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

[aha_1980]

@rohit713

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

[rohit713]

@aha_1980 same problem occur with qstrncpy.

[jsulm]

@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]

@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.