eCos provides compatibility with the ISO 9899:1990 specification for the standard C library, which is essentially the same as the better-known ANSI C3.159-1989 specification (C-89).
There are three aspects of this compatibility supplied by eCos. First there is a C library which implements the functions defined by the ISO standard, except for the mathematical functions. This is provided by the eCos C library packages.
Then eCos provides a math library, which implements the mathematical functions from the ISO C library. This distinction between C and math libraries is frequently drawn — most standard C library implementations provide separate linkable files for the two, and the math library contains all the functions from the math.h header file.
There is a third element to the ISO C library, which is the
environment in which applications run when they use the standard
C library. This environment is set up by the C library startup procedure
(the Section called C library startup>)
and it provides (among other things) a
point function, an
exit() function that
does the cleanup required by the standard (including handlers registered
atexit() function), and an environment
that can be read with
The description in this manual focuses on the eCos-specific aspects of the C library (mostly related to eCos's configurability) as well as mentioning the omissions from the standard in this release. We do not attempt to define the semantics of each function, since that information can be found in the ISO, ANSI, POSIX and IEEE standards, and the many good books that have been written about the standard C library, that cover usage of these functions in a more general and useful way.
The following functions from the POSIX specification are included for convenience:
extern char **environ variable
(for setting up the environment for use with
eCos provides the following additional implementation-specific functions within the standard C library to adjust the date and time settings:
This function sets the state of Daylight Savings Time. The values for state are:
CYG_LIBC_TIME_DSTNA unknown CYG_LIBC_TIME_DSTOFF off CYG_LIBC_TIME_DSTON on
These values will be reflected in the
member of a struct tm. No other meaning is given to
CYG_LIBC_TIME_DSTNA, and in particular it is not
interpreted as any sort of "auto-detect" value, as eCos does not have
the extensive timezone information that would be required in order to
provide this. A call to
tm_isdst set to
CYG_LIBC_TIME_DSTNA) will be treated
as if the supplied time is in UTC, i.e. with neither standard time nor
Daylight Savings Time offsets applied.
This function sets the offsets from UTC used when Daylight Savings Time is enabled or disabled. The offsets are in time_t’s, which are seconds in the current inplementation.
This function retrieves the current setting for Daylight Savings Time along with the offsets used for both STD and DST. The offsets are both in time_t’s, which are seconds in the current implementation.
This function sets the current time for the system The time is specified as a time_t in UTC. It returns non-zero on error.