The C++ libraries depend on the C library for target-specific support. There are no target dependencies in the C++ libraries.

To retarget your C++ streamed I/O, we recommend that you retarget the “_sys_xxxx” driver level functions. These are the functions used by the C and C++ library and are responsible for target specific I/O. The default implementation uses Semihosting to handle I/O on the host machine.

The RVDS Compiler and Libraries Guide discusses which functions have to be re-implemented. A summary is shown below:

_sys_open()
_sys_close()
_sys_read()
_sys_write()
_sys_ensure()
_sys_flen()
_sys_seek()
_sys_istty()
_sys_tmpnam()
_sys_exit()
_ttywrch() 
 
For an example file (retarget.c), used for redirecting C++ streamed I/O to an UART (connected to e.g. a Terminal Emulator), click here.

To retarget standard input/output functionality, low level library functions such as fgetc() and fputc()can be re-implemented instead.

In ADS 1.2 and RVDS 3.x, only functions such as fgetc() and fputc() need to be reimplemented. With RVDS 2.x an additional library function (used by cin) '__fread_bytes_avail()' must also be reimplemented.

The default version of '__fread_bytes_avail()'  fills a buffer by calling fgetc() until either the buffer is filled or EOF is encountered.  Since the retargeted version of fgetc() in the example code simply returns characters from a UART (and never returns EOF), __fread_bytes_avail() must be re-implemented to read a single character by calling fgetc():
 
#ifdef __cplusplus
extern "C"
#endif
size_t __fread_bytes_avail(void *buf, size_t nbytes, FILE *stream)
/* Read a single character into buf[] using fgetc() */
{
  *(char *)buf = (char)fgetc(stream);
  return 1;
}

This function should be added to 'retarget.c' in the Application Note 107  code /RVCT 'emb_sw_dev' example.

For ADS users, general retargeting of I/O functions is described in Application Note 107 , "Embedded Software Development".

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retarget.c