I am trying to build a data logger but rather than using a text file I want it to use a binary file. Is there a library that is available that can already do binary file writes similar to that of C/C++. The plan is to just have the Arduino append the senor readings onto a file contained on a SD card. Then I can pull the SD card and use a computer program, most likely written in C++, to analyze the data.
In the SD library, the function to write to a file takes as an argument a const void * (a pointer to the data, of any type, to write to the file).
If doesn't care what is in that array - binary or ascii (not that there is really a difference). It just copies the data to the file.
This is true of pretty much all filesystems on all operating systems I know of... A file is a vector of bytes, nothing in the filesystem code should care what those bytes are, or what they represent. To the filesystem code "binary file" and "text file" is a meaningless distinction.