QString to unsigned char *

[darksaga]

Hi ppl,

I need to convert a QString to a unsigned char array. I've already searched the forums & did some google reasearch but somehow failed to find a working solution

I had no probs to convert the QString to a normal char array:

QString str = "somestring"; // data comes from a db in my case
int length = str.length();
 
char *sequence = NULL;
sequence = new char[length+1];
strcpy(sequence, str.toLocal8Bit());

QString str = "somestring"; // data comes from a db in my case
int length = str.length();

char *sequence = NULL;
sequence = new char[length+1];
strcpy(sequence, str.toLocal8Bit());

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i think the "unsigned" solution is also pretty simple, but somehow i can't figure it out???

please help...

thx

[marcel]

Do it with QString::toAscii().constData().
It returns a preallocated (const char *) and it is frequently used for these situations.

char *sequence = string.toAscii().constData();

char *sequence = string.toAscii().constData();

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Regards

[jpn]

How can I convert a QString to char* and vice versa ?

[darksaga]

Do it with QString::toAscii().constData().
It returns a preallocated (const char *) and it is frequently used for these situations.

char *sequence = string.toAscii().constData();

char *sequence = string.toAscii().constData();

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Regards

that was exactly what I was looking for, thx @ marcel

now using the following code:

QString str = "ABCD";
int length = str.length();
unsigned char *sequence = NULL;
sequence = (unsigned char*)qstrdup(str.toAscii().constData());

QString str = "ABCD";
int length = str.length();
unsigned char *sequence = NULL;
sequence = (unsigned char*)qstrdup(str.toAscii().constData());

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looked into the QByteArray reference, and would like to know if my assumptions for the example above are correct:

- sequence length = 5 --> ['A'] ['B'] ['C'] ['D'] ['\0']
- sequence is now "independant" from str
- sequence has to be deleted with -> delete [] sequence

????

Regards

[marcel]

Yes, they are correct.
You must delete your (unsigned char*) since you own a copy of the QByteArray buffer.

Regards

[darksaga]

Yes, they are correct.
You must delete your (unsigned char*) since you own a copy of the QByteArray buffer.

Regards

thnx again

[spud]

There is one gotcha with the code above!
The call to toAscii() creates a temporary QByteArray which goes out of scope when used like this:

char *sequence = string.toAscii().constData();
// sequence is now a dangling pointer!

char *sequence = string.toAscii().constData();
// sequence is now a dangling pointer!

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a call like

qstrdup(str.toAscii().constData());

qstrdup(str.toAscii().constData());

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will work, though, since the the pointer isn't accessed after the QByteArray goes out of scope.

To be on the safe side use code like:

const QByteArray ba = string.toAscii(); // make ba const, because modifying this array might otherwise invalidate the pointer
const char *sequence = ba.constData(); 
// now sequence will remain valid within the current scope.

const QByteArray ba = string.toAscii(); // make ba const, because modifying this array might otherwise invalidate the pointer
const char *sequence = ba.constData(); 
// now sequence will remain valid within the current scope.

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[marcel]

There is one gotcha with the code above!
The call to toAscii() creates a temporary QByteArray which goes out of scope when used like this:

char *sequence = string.toAscii().constData();
// sequence is now a dangling pointer!

char *sequence = string.toAscii().constData();
// sequence is now a dangling pointer!

To copy to clipboard, switch view to plain text mode 

a call like

qstrdup(str.toAscii().constData());

qstrdup(str.toAscii().constData());

To copy to clipboard, switch view to plain text mode 

will work, though, since the the pointer isn't accessed after the QByteArray goes out of scope.
[/code]

Correct, of course.
I just wrote the code here, didn't tested it anywhere.

I think it was easy to spot in a program because probably a memory violation would have been raised as soon as the pointer was read the first time.

Regards

[comlink21]

try the following un-tested code;

QString str ="ABCDEFGHIJK";
unsigned char* uca;

uca = new unsigned char[str.length()];
for(int i=0; i<str.length(); i++) uca[i] = str.substr(i,1);

cout<<uca<<endl;

delete [] uca;

comlink21

[marcel]

try the following un-tested code;

QString str ="ABCDEFGHIJK";
unsigned char* uca;

uca = new unsigned char[str.length()];
for(int i=0; i<str.length(); i++) uca[i] = str.substr(i,1);

cout<<uca<<endl;

delete [] uca;

comlink21

What is your point?