istringstream

Hello, I have an istringstream object thats is associated with a string. This string changes and I want the string stream to reflect this change. I tried calling the .str(newstring) function with the new string, but every time I use the extracion operator it fills my variables with garbage. I check the return value of .eof() and it returns true. I tried putting the pointer to the begining using seekg, but that didn''t help. any help would be appreciated thanks also I know that the new string is there because of the .str function.