Atmel CAVR-4 Manual De Usuario

CAVR-4

Part 1. Using the compiler

According to the C standard, your application can interact with the environment using 
the functions 

getenv

 and 

system

.

Note: The 

putenv

 function is not required by the standard, and the library does not 

provide an implementation of it.

The 

getenv

 function searches the string, pointed to by the global variable 

_ _environ

, 

for the key that was passed as argument. If the key is found, the value of it is returned, 
otherwise 0 (zero) is returned. By default, the string is empty.

To create or edit keys in the string, you must create a sequence of null terminated strings 
where each string has the format:

key=value\0

The last string must be empty. Assign the created sequence of strings to the 

_ _environ

 

variable.

For example:

const char MyEnv[] = ”Key=Value\0Key2=Value2\0”;

_ _environ = MyEnv;

If you need a more sophisticated environment variable handling, you should implement 
your own 

getenv

, and possibly 

putenv

 function. This does not require that you rebuild 

the library. You can find source templates in the files 

getenv.c

 and 

environ.c

 in the 

avr\src\lib

 directory. For information about overriding default library modules, see 

If you need to use the 

system

 function, you need to implement it yourself. The 

system

 

function available in the library simply returns -1.

If you decide to rebuild the library, you can find source templates in the library project 
template. For further information, see Building and using a customized library, page 62.

Note: If you link your application with support for I/O debugging, the functions 

getenv

 and 

system

 will be replaced by C-SPY variants. For further information, see 

There are default implementations of the functions 

signal

 and 

raise

 available. If 

these functions do not provide the functionality that you need, you can implement your 
own versions.