How to open binary files on the SD card

[IanKibblewhite]

I need to write and read binary files on the SD card
Text files are no problem. They open with:
FILE *file = fopen(file_name, "w");
But the normal "rb", "rb+", "wb", " wb+" for binary files don't appear to be supported. I get file open errors.
Is there another library I should be using? How do you read and write binary files?
I'd appreciate some direction on this.