c++ - How to check if the (default) value has not been set in the registry -

i need check if (default) value has not been set in registry using c++. whenever value has not been set , try access value, program crashes, , don't know how check if value has been set. here code:

dword valuelength = 256; char* value = new char[valuelength]; auto queryvalueerrorcode = regqueryvalueex(key, null, null, null, (lpbyte) value,         &valuelength); while(queryvalueerrorcode == error_more_data) {     valuelength += 256;     char* newvalue = new char[valuelength];     delete[] value;     value = newvalue;     queryvalueerrorcode = regqueryvalueex(key, null, null, null, (lpbyte) newvalue,             &valuelength); } 

this code doesn't crash - when try access value when crashes, have check if value has been set or not.

the (default) value not exist until has been set, check error code for

error_file_not_found 

before trying access value.