Chapter
6
POSIX API
The best-known API for accessing and managing files and directories is specified within the
POSIX standard (IEEE Std 1003.1). The basis of some of this functionality, in particular
buffered input/output, lies in the ISO C standard (ISO/IEC 9899), though many extensions
provide new features and clarify existing behaviors. Functions and macros prototyped in
four header files are of particular importance:
■
stdio.h . Standard buffered input/output ( fopen() , fread() , etc), operating on FILE
objects.
■
dirent.h . Directory accesses ( opendir() , readdir() , etc), operating on DIR objects.
■
unistd.h . Miscellaneous functions, including working
directory
management
( chdir() , getcwd() ), ftruncate() and rmdir() .
■
sys/stat.h. File statistics functions and mkdir() .
μC/FS provides a POSIX-compatible API based on a subset of the functions in these four
header files. To avoid conflicts with the user compilation environment, files, functions and
objects are renamed:
■
All functions begin with ‘fs_’. For example, fopen() is renamed fs_fopen() ,
opendir() is renamed fs_opendir() , getcwd() is renamed fs_getcwd() , etc.
■
All objects begin with ‘FS_’. So fs_fopen() returns a pointer to a FS_FILE and
fs_opendir() returns a pointer to a FS_DIR .
■
Some argument types are renamed. For example, the second and third parameters of
fs_fread() are typed fs_size_t to avoid conflicting with other size_t definitions.
83