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C99 Compliance Status

shecc implements a subset of C99 suitable for self-hosting and systems programming, prioritizing simplicity, educational value, and minimal dependencies over full standard compliance. This document tracks compliance gaps and non-standard behaviors.

Implemented Features

Core Language

Basic types: int, short, char, void, _Bool
Structures and unions with nested definitions
Enumerations with automatic value assignment
Function definitions and declarations
Arrays (single and multi-dimensional)
Pointers and pointer arithmetic (fully C99-compliant)
Type definitions (typedef)

Control Flow

if/else statements
goto and label statements
while, do-while, for loops
switch/case/default statements
break, continue, return statements

Operators

Arithmetic: +, -, *, /, %
Bitwise: &, |, ^, ~, <<, >>
Logical: &&, ||, !
Relational: <, >, <=, >=, ==, !=
Assignment: =, +=, -=, *=, /=, %=, <<=, >>=, &=, |=, ^=
Increment/decrement: ++, -- (prefix and postfix)
Conditional: ? :
Member access: ., ->
Address/dereference: &, *

Preprocessor (Partial)

#define for object-like and function-like macros
#ifdef, #ifndef, #if, #elif, #else, #endif
#undef for macro removal
defined() operator
__VA_ARGS__ for variadic macros

Missing Features

Storage Classes & Qualifiers

Feature	Status	Impact
`static`	Not implemented	No internal linkage or persistent local variables
`extern`	Not implemented	No external linkage declarations
`register`	Not implemented	No register hint optimization
`auto`	Not implemented	Default storage class (implicit)
`const`	Parsed but ignored	No read-only enforcement
`volatile`	Not implemented	No volatile semantics
`restrict`	Not implemented	No pointer aliasing optimization
`inline`	Not implemented	No function inlining

Type System

Feature	Status	Notes
`long`	Missing	Only 4-byte integers
`long long`	Missing	No 64-bit integers
`unsigned`	Missing	All integers are signed
`signed`	Missing	Implicit for integers
`float`	Missing	No floating-point support
`double`	Missing	No floating-point support
`long double`	Missing	No floating-point support
Bit-fields	Missing	Cannot pack struct members

Literals & Constants

Feature	Status	Current Behavior
Integer suffixes (`u`, `l`, `ll`)	Not parsed	All literals are `int`
Wide characters (`L'c'`)	Not supported	Single-byte only
Wide strings (`L"..."`)	Not supported	Single-byte only
Multi-character constants	Not supported	Single character only
Universal characters (`\u`, `\U`)	Not supported	ASCII only
Hex escapes (`\x...`)	Limited	Max 2 hex digits

Preprocessor Gaps

Feature	Status	Description
`#include`	Parsed only	No file inclusion
Token pasting (`##`)	Missing	Cannot concatenate tokens
Stringizing (`#`)	Missing	Cannot convert to string
`__FILE__`	Missing	No file name macro
`__LINE__`	Missing	No line number macro
`__DATE__`	Missing	No compile date
`__TIME__`	Missing	No compile time
`__STDC__`	Missing	No standard compliance indicator
`#pragma`	Ignored	Accepted but no effect

Advanced Features

Feature	Status	Description
Designated initializers	Missing	No `.field = value` syntax
Compound literals	Partial	Limited support
Flexible array members	Missing	No `[]` at struct end
Variable-length arrays	Missing	No runtime-sized arrays
`_Complex`	Missing	No complex numbers
`_Imaginary`	Missing	No imaginary numbers
`_Static_assert`	Missing	No compile-time assertions
`_Alignof`	Missing	No alignment queries
`_Alignas`	Missing	No alignment specification
`_Generic`	Missing	No generic selection

Non-Standard Behaviors

GNU Extensions

Binary literals: 0b101010
Escape sequence: \e for ESC character
void* arithmetic (treated as char*)
sizeof(void) returns 0 (should be error)
Computed goto

Implementation-Specific

Array compound literals in scalar context use first element
String literals are modifiable (stored in .data, not .rodata)
No strict aliasing rules
Left-to-right evaluation order (not always guaranteed in C99)