Saving of buffers, from a security standpoint

I am working on a bit of code for credit-card processing, so please keep in mind, security of the data is essential.. On part of it i wish to use a buffer, but i wonder if that data is saved anywhere on the running system (as a temp file, etc), or is it just held in the system's memory? My concern is that if an error occurs in the processing, i don't want that buffer to remain (with possible valid Credit Card data) on the system... Colin p.s. As with other 'touchy' subjects like credit card processing, all valid input is appriciated.