C++ zLib compress byte array -

i want compress byte array zlib , here code :

void cggcbotdlg::onbnclickedbuttoncompress() {    // todo: add control notification handler code here    z_const char hello[] = "hello, hello!";    byte *compr;    ulong comprlen;     int returncode;    ulong length = (ulong)strlen(hello)+1;     returncode = compress(compr, &comprlen, (const bytef*)hello, length); } 

but returncode returns -2 (z_stream_error)
took code directly zlib example codes (example.c), works on own example program , returns 0 (z_ok) there in program returns -2
appreciated

you need allocate compression buffer , send size first 2 params, so:

byte compr[somereasonablesize]; ulong comprlen = sizeof(compr); ...