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Joseph Poirier 2015-06-10 16:13:12 -05:00
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@ -403,3 +403,81 @@ The variable RobotIsExploding can be written by your native C program and read
by picoc just like any other picoc variable. In this case it's protected from
being written by the last parameter "IsWritable" being set to FALSE. Set it to
TRUE and picoc will be able to write it too.
# How picoc differs from C90
picoc is a tiny C language, not a complete implementation of C90. It doesn't aim
to implement every single feature of C90 but it does aim to be close enough that
most programs will run without modification.
picoc also has scripting abilities which enhance it beyond what C90 offers.
## C preprocessor
There is no true preprocessor in picoc. The most popular preprocessor features
are implemented in a slightly limited way.
## #define
#define macros are implemented but have some limitations. They can only be used
as part of expressions and operate a bit like functions. Since they're used in
expressions they must result in a value.
## #if / #ifdef / #else / #endif
The conditional compilation operators are implemented, but have some limitations.
The operator "defined()" is not implemented. These operators can only be used at
statement boundaries.
## #include
#include is supported however the level of support depends on the specific port
of picoc on your platform. Linux/UNIX and cygwin support #include fully.
## Function declarations
This style of function declaration is supported:
```
int my_function(char param1, int param2, char *param3)
{
...
}
```
The old "K&R" form of function declaration is not supported.
## Predefined macros
A few macros are pre-defined:
* PICOC_VERSION - gives the picoc version as a string eg. "v2.1 beta r524"
* LITTLE_ENDIAN - is 1 on little-endian architectures or 0 on big-endian architectures
* BIG_ENDIAN - is 1 on big-endian architectures or 0 on little-endian architectures
##Function pointers
Pointers to functions are currently not supported.
##Storage classes
Many of the storage classes in C90 really only have meaning in a compiler so
they're not implemented in picoc. This includes: static, extern, volatile,
register and auto. They're recognised but currently ignored.
## struct and unions
Structs and unions can only be defined globally. It's not possible to define
them within the scope of a function.
Bitfields in structs are not supported.
## Linking with libraries
Because picoc is an interpreter (and not a compiler) libraries must be linked
with picoc itself. Also a glue module must be written to interface to picoc.
This is the same as other interpreters like python.
If you're looking for an example check the interface to the C standard library
time functions in cstdlib/time.c.
## goto
The goto statement is implemented, but only supports forward gotos, not backward.
The rationale for this is that backward gotos are not necessary for any
"legitimate" use of goto.
Some discussion on this topic:
* http://www.cprogramming.com/tutorial/goto.html
*http://kerneltrap.org/node/553/2131