FAQ-0298 How do I convert an 8-bit descriptor to a Java string?


FAQ-0298 How do I convert an 8-bit descriptor to a Java string?

» Symbian OS » Developer Knowledgebase » FAQ-0298

Classification:	Java	Category:	JNI
Created:	10/12/99	Modified:	07/03/2001
Number:	FAQ-0298
Platform:	Not Applicable

Question:
How do I convert an 8-bit descriptor to a Java string?

Answer:
To get a jstring (which can be returned to the Java side) from a TPtr8 (or TBuf8) descriptor, you can use the following code:

TPtr8 buf;
...
const TText8* ptr = buf.PtrZ();
jstring str = aJNI->NewStringUTF(REINTERPRET_CAST(const char*, ptr));
If you have a TPtrC or a TBufC descriptor, you will not be able to access the PtrZ() method directly, but you can do this through an intermediate TPtr8 as follows:

TPtrC8 bufC;
...
TPtr8 buf = bufC.Des()
const TText8* ptr = buf.PtrZ();
jstring str = aJNI->NewStringUTF(REINTERPRET_CAST(const char*, ptr));
Similarly for an HBufC8 heap descriptor:

HBufC8* bufC;
...
TPtr8 buf = bufC->Des();
const TText8* ptr = buf->PtrZ();
jstring str = aJNI->NewStringUTF(REINTERPRET_CAST(const char*, ptr));

Notes:

1. The PtrZ() serves to append a null terminator to the string to which it is applied and return a const pointer to unsigned data. You must ensure that there is enough space in the buffer for the null to be appended, other a User 23 Panic will occur.

2. The REINTERPRET_CAST is necessary because ptr is a pointer to unsigned data whereas the constructor for a Java string requires a pointer to (null-terminated) signed data.

3. If the EPOC descriptor contains cp1252 special characters, the conversion should be done via an intermediate 16-bit buffer descriptor. The details of how to do this under ER5 are given in the following KB entry dealing with conversion in the opposite direction. The further conversion from a 16-bit descriptor to a Java string is described here .