Conceptually, the C library can be divided into functions that are part of the ISO C Language specification and functions that provide support to the ISO C language specification. This is shown in Figure 2.2.

Support for some ISO C functionality is provided by the host debugging environment at the device driver level.

For example, the RVCT C library implements the ISO C printf() family of functions by writing to the debugger console window. This functionality is provided by calling __sys_write(). This is a support function that executes a semihosting call, resulting in a string being written to the console.