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Description (Version 1 - not maintained anymore)

C' is a extended C compiler that generates readably C code.

See it online: http://www.thradams.com/web/cprime.html

C language extensions tour

Struct members with initializers

struct Point
{
  int x = 1;
  int y = 2;
};

Default initializer

int main()
{
  struct Point pt = {}; //same as {.x = 1, .y = 2}
}

Lambda Expression

This is similar of C++. The diference is that we don't capture and the result of the lambdas expression is always a pointer to function.

void Run(void (*callback)(void*), void* data);
int main()
{  
  Run([](void* data) {
    printf("first");
    Run([](void* data){
      printf("second");
    }, 0);     
  }, 0);
}

the generated code is :

void Run(void (*callback)(void*), void* data);

static void _lambda_1(void* data){
      printf("second");
    }

static void _lambda_0(void* data){
  
    printf("first");
    Run(_lambda_1, 0);     
  }

int main()
{  
  Run(_lambda_0, 0);
}

Function tags

Functions can have a extra identifier that is called function tag.

void FunctionName(int) : functionTag;

Function can be tagged in one place

void FunctionName(int) : functionTag;

//this is the same function with the same tag
void FunctionName(int); 

Explicit function instantiation

The compiler knows how to implement some functions for any struct.

They are:

• init - initialize structs with default values
• destroy - free resources used by structs
• create - Allocates and initialize the object on the heap (malloc)
• delete - Destroy a object created on heap and frees the memory

Any of these functions can be implemented automaticaly for any struct.

It is called explicit instantiation because declaration and point of instantiation is given by the programmer.

Declaration sample:

//file X.h
struct X {
    int i = 3;
};

struct X * makeX() : create;

Instantiation sample:

The compiler will understand that makeX is instance of 'create' reading the function tag. The instantiation point is defined with the keyword default.

//file X.c
#include "X.h"

//this is the point of instantiation
struct X * makeX() default;

Auto pointer qualifier

Pointers can be qualified with the 'auto' keyword.

This tells the compiler that the pointer is the owner of the pointed object.

In pratice this is used for destroy and delete instantiation:

For instance:

struct X {
    char * auto Text;
};

void DestroyX(struct X *) : destroy;

The destroyX instantiation will be

void DestroyX(struct X *) default
{
    free((void*)->Text);
}

Pointer qualifier [size]

Structures member pointers can be qualified with '[size]' .

This tells the compiler that the pointer is pointing size objects where size is also a member of the struct.

struct Item {
	char * auto Text;
};

struct Items {
	struct Item * auto * auto [Size] pData;
	int Size;	
};


void Items_Destroy(struct Items* pItems) : destroy;

This 'struct Item * auto * auto [Size] pData;' can be read as "pData is a onwer pointer of Size onwer pointers of struct Item".

Items_Destroy is instanciated as:

void Items_Destroy(struct Items* pItems) default
{
    if (pItems->pData)
    {
        for (int i = 0; i < pItems->Size; i++)
        {
            free((void*)pItems->pData[i]->Text);
        }
        free((void*)pItems->pData);
    }
}

Automatic function tags

This is an optional feature controled by compiler flags. We can define that functions with the aproprieted signature and know suffixes like create, init, destroy and delete (case insensitive) will be automatically tagged.

For instance:

void Items_Destroy(struct Items* pItems);

Is automatically tagged as

void Items_Destroy(struct Items* pItems) : destroy;

Automatic instanciation of Push

Push is a function that adds a new item inside a known data structure.

It cannot be instanciated for any type. The current implementation allow the instanciation of push for vector and linked list only.

struct Item {
    int i;
    struct Item* pNext;
};

struct Items {
    struct Item* pHead,* pTail;
};

void Items_Push(struct Items* pItems, struct Item* pItem) : push;

Instantiation for linked list with pHead and pTail

void Items_Push(struct Items* pItems, struct Item* pItem) default
{
    if (pItems->pHead == 0)
    {
        pItems->pHead = pItem;
    }
    else
    {
        pItems->pTail->pNext = pItem;
    }
    pItems->pTail = pItem; 
}

struct Item {
    int i;
    struct Item* pNext;
};

struct Items {
    struct Item** pData;
    int Size;
    int Capacity;
};

void Items_Push(struct Items* pItems, struct Item* pItem) : push default;

void Items_Push(struct Items* pItems, struct Item* pItem) default
{
    if (pItems->Size + 1 > pItems->Capacity)
    {
        int n = pItems->Capacity * 2;
        if (n == 0)
        {
            n = 1;
        }
        struct Item** pnew = pItems->pData;
        pnew = (struct Item**)realloc(pnew, n * sizeof(struct Item*));
        if (pnew)
        {
            pItems->pData = pnew;
            pItems->Capacity = n;
        }
    }
    pItems->pData[pItems->Size] = pItem;
    pItems->Size++;
}

Especial comments

CPrime has especial comments that are ignored.

/*@   and   */

These two sequences will be interprted as spaces.

These special comments where created to allow C language extensions be created using normal C syntax.

For instance, this C code parsed by C compiler will see comments

//file X.h
struct X {
    int i /*@= 3*/;
};

struct X * makeX() /*@: create*/;

but cprime compiler will see:

//file X.h
struct X {
    int i = 3;
};

struct X * makeX() : create;

CPrime is compiled using itself. I use VC++ compiler and IDE with this annotation method. Without this method I would need a IDE plugin, and this is something I dont have at this time.

Runtime polymorphism

In C we have void * that means a pointer to any object. In C' we can espcify a list of possible pointed objects.

Sample:

struct Box {
    int id = 1;
};

struct Circle {
    int id = 2;
};

struct <Box | Circle> Shape {
    int id;
};

struct Shape * p ...;

Here, p is a pointer to Box or Circle. The struct Shape is manually (at this point) defined with the comom initial member of Box and Circle and this member is called discriminant.

Having the discriminant we can instanciate functions for Shape.

void Shape_Draw(struct Shape* pShape) default;

resulting in:

void Shape_Draw(struct Shape* pShape) default
{
    switch (pShape->id)
    {
        case  2:
            Circle_Draw((struct Circle*)pShape);
        break;
        case  1:
            Box_Draw((struct Box*)pShape);
        break;
        default:
        break;
    }
}

Using the compiler

The compiler can be used together with traditional C compilers like VC++, clang or gcc.

Grammar changes

Background

I work professionally with C++ since 2000 keeping my knowledge about C++ updated. After 2014 I noticed that my interest for the C language was gradually increasing.

In 2010, I opened a topic in com.lang.C++.moderated about the possibility of to have “smart pointers” inside the C++ type system and later in 2015 I watched the Herb Sutter presentation cppcon “Writing Good C++14 By Default" where he talks about memory ownership checked statically. After this point I became very motivated to implement the checked ownership analysis in the C language as part of the type system and I started to write my C parser in C.

During the development of this parser and static analysis, I had some difficulties with the C language that have already begin addressed by C++, like to generate special member functions. I was doing constructors and destructor by hand and wondering how they could be designed and used in C.

At some point I decided that I should address the problem to work better with C before to do the static analysis and then I renamed the project to C’ cprime. Because I want a tool to be useful now (not something experimental) I spent some time to solve the problem of generating C code from C code including the preprocessed parts. This allowed me to use existing C compilers and IDEs. C’ can generate destructors for structs and can have owner pointers in the type system. The motivation for static analysis still there and it is also related with code generation. More motivations like containers and polymorphism are included in the C’ as well.

Historical references

[1]

My message to comp lang cpp moderated

https://groups.google.com/g/comp.lang.c++.moderated/c/_9OtpMx9wnk/m/6VIXyvTsRnEJ

It would be better if unique_ptr were a type modifier? - "Jul 24, 2010, 10:55:22 AM"

It Would be better if unique_ptr were a type modifier?
C++ has many type modifiers line mutable, const, volatile.

In my code I use very few of mutable and even less of volatile
modifier.
In the other hand, the concept of unique pointer I use all the time.

positive points:

- A clear language concept instead of library
- no includes
- Some help to compiler, to generate fast code. (I'm not sure about
that)
- Better error message generated by compiler

I guess that the shared_ptr is also a candidate for a type modifier
but with much more details and implications.

What do you think?

Thiago...

Any path who calls the destructor must be checked by the compiler to
see if the pointer is null, including exceptions, returns, goto etc...
One problem is that compilers could differ how smart they are do
detect this and them the code would be different in each compiler. The
delete before destructor should be very straightforward to have
agreement of all compilers, and the smart pointers would be used as
well to call this delete and tell the compiler that the code is safe.
At this point it seems that the solution returns to smart pointers
again, or the "deleter" should be part of the modifier.