Checking character types. Handling strings. Doing maths.
The libraries in GCC contain a repertoire of standard functions and
macros. There are many different kinds of function and macro in the
libraries. Here are a few of the different kinds available, with the
header files you can use to access them:
Character handling: ctype.h
Mathematics: math.h
String manipulation: string.h
You may find it useful to read the header files yourself. They
are usually found in the directories /usr/include and its
subdirectories on GNU/Linux systems. The three header files listed
above can be found in /usr/include; there is a second version of
ctype.h in /usr/include/linux.1
The version of
ctype.h in the /usr/include directory proper is the one
that comes with glibc; the one in /usr/include/linux is a
special version associated with the Linux kernel. You can specify the
one you want with a full pathname inside double quotes (for example,
#include "/usr/include/linux/ctype.h"), or you can use the
-I option of gcc to force GCC to search a set of
directories in a specific order. See Building a library, for
more information.)
